Psychological & Behavioral Intelligence

Kasan Allegedly Murdered by Susumu Terauchi, Hakata, Fukuoka, Japan

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Human-reviewed analysis

Psychological & Behavioral Intelligence

This source-based behavioral analysis does not establish a clinical diagnosis, motive, or legal finding.

Case Overview

The source describes a reported progression from jealousy and location monitoring to breakup resistance, repeated unwanted contact, grievance, pursuit, lethal violence, flight, and later remorse. This is behavioral analysis based on a narrated video report, not a clinical evaluation. No professional diagnosis is reported for either central participant.

Relationship Dynamics

The relationship reportedly began secretly because of an employer dating prohibition and became increasingly unequal after Terauchi monitored Kasan's location and resisted her attempt to leave. Kasan sought help from friends and police, while Terauchi allegedly reframed the consequences of his conduct as unfair treatment of himself. The reported restraining order, continued contact, threats, workplace confrontation, and final pursuit indicate escalating coercive and grievance-based dynamics.

Escalation Summary

The reported pathway moved from secret dating and jealousy to digital monitoring, intoxicated harassment, attempted separation, police intervention, continued contact despite restrictions, perceived provocation, confrontation, pursuit, stabbing, flight, and post-incident remorse. The source leaves the degree of advance planning at the station disputed.

Observed Patterns and Case-Specific Context

Each entry separates the reported behavior or state from the analytical strength of the available narration.

Behavior / construct	Person / subject	Detailed case context	Evidence
Possessiveness or monitoring Control dynamics	Susumu Terauchi AccusedLover of victim	Terauchi reportedly introduced continuous location monitoring into the relationship. The behavior reduced Kasan's privacy and preceded her growing suspicion and disclosure to friends. It is a concrete control-related behavior rather than a clinical conclusion. Context or trigger: During the secret dating relationship, before Kasan attempted to separate. Reported expression: The source reports that Terauchi used a smartphone application to know Kasan's location at all times. This behavior is presented as part of his jealousy and intrusive monitoring.	Explicitly reported Confidence: High
Infidelity or competing attachment Relationship stressor	Case-wide	The relationship was described as secret because of workplace rules, not because either participant was reported to have another romantic partner. Terauchi's monitoring and accusations should therefore not be converted into a finding of infidelity. The available material supports jealousy and control, but not an affair construct. Context or trigger: The source describes jealousy but does not report an affair or competing romantic attachment. Reported expression: No competing attachment is established in the account. Terauchi's jealousy appears directed toward Kasan's independence and possible outside contacts, but the source does not identify an actual rival.	Insufficient information Confidence: Indeterminate
Separation or abandonment threat Loss or threat	Susumu Terauchi AccusedLover of victim	Kasan's effort to leave appears to have been experienced by Terauchi as a significant loss or grievance. Rather than accepting separation, he allegedly continued contact and pursuit. His reported later explanation linked the violence to refusal of reconciliation, although that statement does not excuse or prove the attack's full motive. Context or trigger: Kasan attempted to end the relationship in October 2022 and later sought police assistance. Reported expression: The source says Terauchi did not accept the breakup and continued pursuing contact. He later reportedly stated that he attacked Kasan because she would not reconcile.	Narrative-supported psychological state Confidence: High
Coercive control Control dynamics	Susumu Terauchi AccusedLover of victim	The reported conduct extended beyond ordinary relationship conflict into repeated efforts to control Kasan's movements and access to her. The restraining order and her attempt to use police protection did not end the reported behavior. This pattern is consistent with coercive control as a behavioral construct, without requiring a clinical diagnosis. Context or trigger: After Kasan became uncomfortable and attempted to stop contact. Reported expression: Reported behaviors included location monitoring, refusal to accept the breakup, repeated contact, demands to meet, a workplace confrontation, and continued pursuit despite a restraining order.	Narrative-supported psychological state Confidence: High
Emotional abuse Control dynamics	Susumu Terauchi AccusedLover of victim	Terauchi reportedly shifted attention from Kasan's fear and safety to his own grievance about employment and reputation. His demands and hostile communications appear to have increased pressure on Kasan after she sought help. The source supports a pattern of emotionally harmful conduct, though it does not provide a complete history of the relationship. Context or trigger: Conflict after Kasan contacted police and attempted to end the relationship. Reported expression: The source reports hostile messages, demands that Kasan meet him, anger about police involvement, and statements that she owed him an apology.	Narrative-supported psychological state Confidence: Moderate
Deception or concealment Behavioral pattern	Susumu Terauchi AccusedLover of victim	Concealment appeared at several points in the narrated sequence. The initial secrecy was shared by the couple because of workplace rules, whereas the later disguise and false-name use are attributed to Terauchi after the conflict and homicide. The source does not establish the precise purpose of every concealment behavior. Context or trigger: The secret workplace relationship and later confrontations. Reported expression: The relationship was reportedly concealed from the employer, Terauchi allegedly appeared at the workplace in disguise, and he later used a false name while hiding in an internet café.	Explicitly reported Confidence: High
Family-system conflict Family dynamics	Case-wide	The source presents external pressures around the relationship, including an employer rule and Kasan's responsibilities to her child and parents. These factors do not establish that family members caused the homicide. They help explain the broader social and practical context in which the relationship and its disclosure unfolded. Context or trigger: The relationship was affected by the employer's dating prohibition and Kasan's family responsibilities. Reported expression: Kasan reportedly supported her parents financially and was raising a daughter, while the workplace imposed a dating rule that placed a fine on the male employee.	Narrative-supported psychological state Confidence: Moderate
Anger or resentment Emotional state	Susumu Terauchi AccusedLover of victim	Terauchi reportedly interpreted consequences of his conduct as an injustice against himself. His anger was directed toward Kasan, police involvement, employment consequences, and public criticism. This grievance framing accompanied continued contact and preceded the fatal confrontation. Context or trigger: Police involvement, workplace consequences, public labeling as a stalker, and Kasan's refusal to reconcile. Reported expression: The source reports angry workplace confrontation, resentment toward Kasan and police, threats to hate her for years, and complaints that he was being unfairly blamed.	Narrative-supported psychological state Confidence: High
Moral disengagement Cognitive pattern	Susumu Terauchi AccusedLover of victim	The reported blame-shifting reduced Terauchi's responsibility in his own account by making Kasan's relationship decision part of the explanation for the violence. This is consistent with moral disengagement as an analytical construct. It remains a description of reported statements, not a conclusion about his complete psychological state. Context or trigger: The homicide investigation and interrogation. Reported expression: Terauchi reportedly said that Kasan's refusal to reconcile contributed to the stabbing and that she was partly at fault. The source presents this as an attempt to justify his conduct.	Narrative-supported psychological state Confidence: High
Emotional escalation Escalation	Case-wide	The case narrative describes increasing intensity over time rather than a single isolated disagreement. Protective intervention was followed by alleged continued contact and a later public pursuit. The final attack represented the most severe reported point in that escalation. Context or trigger: The transition from jealousy and unwanted contact to a final confrontation. Reported expression: The reported sequence included monitoring, intoxicated harassment, breakup resistance, police reporting, workplace confrontation, continued messages, perceived provocation, pursuit, and repeated stabbing.	Narrative-supported psychological state Confidence: High
Impulsive aggression Planning or impulsivity	Susumu Terauchi AccusedLover of victim	The final confrontation included rapid verbal escalation and physical pursuit. Although the source also reports a disputed question about planning, the attack itself followed an immediate confrontation and was described as a sudden transition to weapon use. The available account cannot determine how much advance preparation preceded the event. Context or trigger: The station confrontation after Kasan tried to leave and suggested discussing the matter at a police station. Reported expression: The source reports that Terauchi followed Kasan, shouted at her, became more aggressive, removed a knife, and stabbed her repeatedly.	Narrative-supported psychological state Confidence: Moderate
Premeditation and planning Planning or impulsivity	Susumu Terauchi AccusedLover of victim	The concealed knife and location on Kasan's route were treated by prosecutors as indicators of preparation. Terauchi denied lying in wait, and the court reportedly found no decisive evidence proving that point. Planning is therefore supported as a disputed investigative interpretation rather than an uncontested fact. Context or trigger: The disputed presence near Hakata Station and possession of a concealed knife. Reported expression: Prosecutors reportedly argued that Terauchi waited along Kasan's route home and had planned the attack, while the defense claimed the encounter was accidental and the knife was for self-defense.	Analytical inference Confidence: Moderate
Detection avoidance or evasion Post-offense behavior	Susumu Terauchi AccusedLover of victim	The reported post-incident behavior involved movement away from the scene and concealment of identity. These actions are consistent with avoiding immediate detection or accountability. The source does not establish his internal motive for fleeing, but the sequence is behaviorally clear as narrated. Context or trigger: Immediately after the reported stabbing. Reported expression: Terauchi reportedly fled, went to an internet café, used a false name, and hid before police found and arrested him.	Explicitly reported Confidence: High
Grief and bereavement Emotional state	Kasan VictimLover of offender	The family response was described as profound grief following Kasan's death. The mother's court statement conveyed both emotional loss and the practical impact on the family. The source does not provide a clinical assessment of the mother or child. Context or trigger: Kasan's death and the subsequent court proceedings. Reported expression: The source reports that Kasan's mother described a hole in the family's hearts and the loss of future memories. She also reported that Kasan's daughter was too shocked to attend school.	Explicitly reported Confidence: High

Behavioral Escalation Pathway

Select a stage to expand it; scroll horizontally to follow the full sequence.

Narrative sequence

1 Secret relationship begins Kasan and Susumu Terauchi Relationship decision process Explicitly reported

The source reports that the pair met through related workplaces, began dating after Terauchi's confession, and concealed the relationship because their employer prohibited employee dating. This created a relationship context shaped by secrecy and workplace consequences.

Explicitly reported · High confidence

2 Monitoring and jealousy Susumu Terauchi AccusedLover of victim Possessiveness or monitoring Explicitly reported

Terauchi reportedly used a smartphone application to track Kasan's location. Kasan became suspicious and discussed the behavior with friends, indicating that the relationship had become intrusive before the final incident.

Explicitly reported · High confidence

3 Breakup attempt Kasan and Susumu Terauchi Separation or abandonment threat Narrative-supported psychological state

After an alleged intoxicated harassment episode in October 2022, Kasan told Terauchi to stop calling and attempted to end the relationship. The source says he did not accept the breakup, leaving Kasan to seek outside help.

Narrative-supported psychological state · High confidence

4 Police and workplace intervention Kasan VictimLover of offender Help-seeking or disclosure Explicitly reported

Kasan reportedly went to police and the relationship became known at her workplace. A manager told Terauchi to stay away, and police issued an emergency restraining order under the Anti-Stalking Law.

Explicitly reported · High confidence

5 Continued grievance and contact Susumu Terauchi AccusedLover of victim Anger or resentment Narrative-supported psychological state

Despite the reported order, Terauchi allegedly continued contacting Kasan and expressed long-term hatred. He also reportedly interpreted an anonymous emoji message as provocation and complained that he alone was being blamed.

Narrative-supported psychological state · High confidence

6 Public confrontation and pursuit Susumu Terauchi and Kasan Emotional escalation Narrative-supported psychological state

On January 16, 2023, the source reports that Terauchi confronted Kasan near Hakata Station, followed her when she tried to leave, and chased her for approximately 173 meters. Kasan reportedly proposed discussing the issue at a police station, but the confrontation intensified.

Narrative-supported psychological state · High confidence

7 Fatal weapon attack Susumu Terauchi AccusedLover of victim Impulsive aggression Narrative-supported psychological state

The source reports that Terauchi removed a knife and stabbed Kasan repeatedly in the chest and head, reportedly at least 17 times. The account presents this as the focal incident, while the degree of advance planning remained disputed at trial.

Narrative-supported psychological state · High confidence

8 Flight and post-incident remorse Susumu Terauchi AccusedLover of victim Detection avoidance or evasion Narrative-supported psychological state

After the stabbing, Terauchi reportedly fled to an internet café, used a false name, and hid. During later questioning, he reportedly cried after learning that the incident occurred on Kasan's birthday and expressed regret, although the judge later characterized his remorse as superficial.

Narrative-supported psychological state · Moderate confidence

Arrows show the sequence described in the source narrative; they do not prove that one psychological state caused the next event.

Source Limits and Cautions

The account is a translated or adapted video narration rather than a primary court record. Some psychological descriptions are narrator interpretations, and the source does not provide complete police files, forensic findings, independent witness testimony, or clinical assessments. Behavioral patterns described here do not establish legal guilt or psychological causation beyond the reported facts.

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