I've actually not looked too closely at Megami no Oni myself, so I'm not 100% sure what he gets up to there. At the very least, he seems like a nice enough guy. A bit like how Shoukirou managed to turn himself around while still acknowledging his faults; I could see that being the reason Eiichi would be living on Sakoku island as it's "caretaker" as Ume puts it.