You're Not a Replacement

A mentor-student relationship, where the mentor, Gojo starts acting upon his past trauma when he sees a student who doesn't actually look like HIM at all.

But the way he talks, walks, laughs and frowns when frustrated is way too similar for comfort.

Jujutsu kaisen is owned by Gege Akutami. This short story is merely a fan-fiction.
The cover art isn't mine. I found it on pinterest.