Serizawa is litrally one of my favorite characters in all of mob psycho and here's why:
1. His character is very relateable to me as an autisic person, even though I haven't gotten to around his age. I also relate to hom with his bad experience with counslers/therapists (unfourtunantly)
2. His character development. Serizawa goes from a deeply anxious man, a pawn to claw and incapable without Tochiro and his umbrella to a man who's able to handle clients at spirits and such! It makes me so happy to see how far he came!
3. He is really sweet, he leaves claw due to him not wanting to harm anyone. Once mob pulled him back to reality he was unable to stay in the organization due to Tochiro's goal. The main reason he locked himself in is due to his fear of hurting others. Which is really sad and really sweet.
There's probably more but I just forgor.