Biodata
| Feature | Value |
|---|---|
| Name | Masamichi Yaga (夜蛾正道) |
| Alias(es) | Mr. Yaga; Yaga-sensei 24 31 |
| Gender | Male |
| Affiliation | Tokyo Jujutsu High 16 |
| Occupation/Role | Jujutsu sorcerer; first-year homeroom teacher; instructor in jujutsu theory and practical training 16 26 36 38 |
| Status | Alive and teaching in the supplied chapters 49 |
| First Appearance | First on-page appearance in his office during Yan Si and Suguru Geto’s enrollment 16 |
Appearance
Yaga has a tall, imposing build and a square, stern face. His thick-knuckled hands handle paperwork with surprising delicacy, prompting Yan Si to think of him as a “burly warrior threading a needle” 16 26.
- Voice: Deep, with a commanding delivery during lessons and disciplinary announcements 22 31.
- Clothing: Wears a dark gray cardigan over a black turtleneck, paired with leather shoes, on the first official day of classes 36.
- Mannerisms: Often stands with his arms crossed or his hands behind his back; a twitching temple and increasingly forceful grip betray his frustration 23 26 31.
Personality
Yaga is stern and methodical, but his decisions reflect concern for his students’ safety rather than discipline alone. He warns the first-years that sorcery carries a high mortality rate and that some may not survive to graduate. He also refuses to force Shoko, whose intended role is medical support, into an unsuitable fight with Yan Si 24 28.
He distinguishes talent from good judgment. Although he recognizes the incoming class as exceptionally gifted, reading their files leaves him awake for three hours. Gojo’s open defiance and Yan Si’s smiling unpredictability trouble him more than their abilities impress him 23 25 30.
His patience has clear limits. When explanations fail, he turns to cleanup assignments, threats of additional punishment, and blows to the head. Even so, he approves of ordinary camaraderie, including Yan Si sharing sunflower seeds with Shoko 26 31 36.
Abilities & Skills
Jujutsu Instruction
Yaga breaks abstract concepts into manageable parts, using progressively developed blackboard diagrams and occasional physical samples 37.
- Teaches the nature and classification of cursed energy, including its relationship to negative emotions and curse formation 36.
- Insists on reviewing fundamentals even when advanced students claim to have memorized the material, because Yan Si lacks formal grounding 36.
- Supplies Geto with a basic jujutsu theory textbook before classes begin 17.
Student Assessment
Yaga combines enrollment files, mission reports, and direct observation to evaluate each student’s capabilities and risks 25 28 30.
- Physical combat: Organizes Gojo and Geto’s hand-to-hand test without Limitless or controlled cursed spirits 26 27.
- Reaction testing: Replaces the proposed Yan Si–Shoko spar with a wooden-rod evasion test better suited to their roles 28 29.
- Individual restrictions: Forbids Yan Si from using cursed tools or relying on Reverse Cursed Technique to absorb hits during the evasion assessment 29.
- Cursed energy analysis: Uses a measuring device to assess output quality and control precision; identifies Geto’s slight fluctuations and Yan Si’s irregular readings 38.
Cursed Energy and Physical Discipline
Yaga releases a small amount of cursed energy as a warning when his students exhaust his patience. Everyone present can feel the resulting pressure 26.
- Delivers disciplinary blows to Gojo and Yan Si’s heads after they disrupt class 36.
- His strength is also evident when he snaps chalk and dents the edge of his notebook through his grip 24 31.
- The supplied chapters do not establish his sorcerer grade or identify an innate cursed technique.
Relationships
- Yan Si — Student requiring particular attention. Yaga distrusts his harmless-looking smile after reviewing reports of reckless combat and pranks. By Yan Si’s unauthorized departure, his concern has escalated from classroom misconduct to a potentially dangerous disregard for rules 25 29 49.
- Satoru Gojo — Exceptionally gifted but openly defiant student. Yaga recognizes the significance of Six Eyes and Limitless while repeatedly shutting down Gojo’s attempts to reinterpret restrictions or propose unsafe experiments 25 31 38.
- Suguru Geto — Initially the most dependable-looking student. Yaga values his politeness, restraint, and underlying resolve, but reserves judgment after observing how readily he accommodates Yan Si’s habits 25 30.
- Shoko Ieiri — Medical-support student whose quietness Yaga interprets as reluctance to expend effort rather than obedience. He adapts her assessment to her intended role, but still assigns punishment when she smokes in front of him 25 28 31.
Story Role / Major Arcs
Enrollment and Orientation
Yaga handles the final paperwork for Yan Si and Geto, stamping their forms to formalize enrollment. At this point, he is their future homeroom teacher; Hatoyama Jushō is Tokyo Jujutsu High’s principal 15 16.
The full class’s first meeting immediately becomes chaotic as Gojo and Yan Si encourage each other’s jokes and arrange a fight. Yaga interrupts their banter to explain the dangers of sorcerer work and emphasize that missions are not entertainment 22 23 24 25.
Basic Assessments and School Rules
Yaga conducts the first-years’ physical assessments, ultimately recording an “Excellent” result for Yan Si’s evasion performance despite his concerns about the student’s behavior 26 30.
After testing, he establishes that sparring requires a teacher’s presence and must take place on the training grounds. Gojo and Yan Si’s loophole-seeking questions earn them cleanup duty alongside Shoko. A later suggestion that Yan Si frighten Yaga results in three days of training-ground cleanup 31 33.
Formal Lessons and Unauthorized Mission
During the first official lessons, Yaga balances basic theory with practical cursed energy testing. He rejects Gojo’s proposals to use Yan Si to draw curses to Tokyo Tower or the school, citing the danger to the school’s barrier and threatening Gojo’s allowance 36 37 38.
Yan Si later leaves with an assistant supervisor for a mission without requesting leave or following the usual procedures. On discovering the absence, Yaga treats the incident as more than truancy: Yan Si’s apparent indifference to established rules makes him an unpredictable variable in a society whose leadership resists such uncertainty 47 49.