I get the feeling that we'll be seeing more of his isekai partners, they might just come visit him on Earth. I might be completely wrong, but it's one of those Chekov's guns situation. Like with the chained up black wing. Ain't no way he ain't unleashing his hidden power and it somehow is some absolutely destructive offensive capability.
Also, now we have the genki childhood friend who's really into him. Meanwhile the first heroine ended up being the silent stalker girl who may also be a childhood friend due to the hints that're being dropped.
Hell at this point I expect that there's at least one female childhood friend from each of the major houses that're going to be part of his harem.
Yes, I know there's no harem tag. But it sure won't stop the girls around him from forming one.