I wonder if it's gonna turn out that he himself dealt in something like the suffering/death/exploitation of Yokai to build the riches he possesses, of if it'll have been his family, with him as the sole heir to all this blood money - and he tried to kill himself in shame over it, being utterly remorseful but otherwise having nothing to do with how the wealth was accrued.
Since I'm guessing that's the overarching line being drawn here, more than ever after that dream of his that kicks off this chapter. I guess it could be humans and not yokai that were exploited, but the tie-in to the history surrounding the relationship between humans and Yokai feels too pointed to overlook and expect something else to be involved in his backstory.