Btw, if you look at the mysterious person's trousers, it's the same type that Ebisu wore in chapter 26 when the teacher trio and Mi-kun met in Kyoto. We know Haru was a top student back in his university years, naturally he should graduate at 22 and find a job at 23. But he only became a teacher in 24 then dropped out after 30 minutes out of fear, then stayed at home for a year until the start of the manga. Question is, what did he do in 23?
Currently, a theory raising in Vietnamese community is that Haru's first job was at the secondary school Sano studied. Based on Sano's flashbacks, he went to the same school as Ebisu, but an incident happened and he had to transfer to Hyakki Academy for highschool. That incident highly likely was related to Haru but his memory about that part was erased. It would also explain why Amaako was so against him teaching and Papaaki, knowing his son was being aimed at, called the principle and asked him to take Haru in to protect under the guise of hiring a new teacher.
Of course, this is just a theory I parroted
