[@Medjedovic] To be more specific, he knows that Maruto was an underdog of the R&D division,  despite being regarded as a genius. The reason was that he kept refusing to work on projects that required live specimen experimentation, 'cause he couldn't stand to port innocent Youkai to suffering.

He also had a daughter that was very ill and lived at one of YTC's owned hospitals, being that the main train why he still worked for the company. 

Not much of his fate is known now, other than that he left YTC a couple months before Ayato, right after his daughter's death.

EDIT: Oh yeah, also Maruto was part of a small band of YTC employees and owned the same custom Les Paul that Eos now have ever since he was in his highschool's music club.