Episode 9 of “Cells at Work” is titled “Thymocyte”, where an argument between Helper T Cell and Killer T Cell led to a revelation of their past interactions in the thymus.
Anime: Hataraku Saibou, Cells at Work, はたらく細胞
Image sources:
All scenes are taken from “Cells at Work” unless otherwise stated.
Images of body systems are drawn by me.