Reasoning, and then being blasted by the neighboring idol

It is impossible for humans to become younger.
However, the high school detective Gensuke Miura, who was reincarnated in Tokyo, discovered that his neighboring classmate Asano Mio was acting abnormally.
Her body was becoming infantile at an extremely fast rate, and she was even at risk of turning into a baby or even disappearing.
All this seems to be related to the increasingly frequent mysterious phenomena in Tokyo.
After her body changes were revealed, Asano Mio made a strange request to Miura Gensuke after school.
From then on, Miura Gensuke's life gradually went off track...
Remember, living in Tokyo today, anything normal is abnormal.