White haired man

The white haired man appears before the closing credits at the end of the anime at episode 13.

He appears to resemble Maniwa, changed drastically after his epic confrontation with Shonen Bat when he is absorbed by the darkness.

He resembles the old man who died in the second half of the anime. Maniwa had followed the path of the Ancient Master which guided him to the truth.

The man is seen at the end writing complex equations on pavement (probably also outside the hospital) just as the old man had been doing at the start.