This mc will certainly keep mating left and right in this world and pursuing your ideals Abe-san, your mission lives on still. I just wonder if any of them will actually get pregnant though.
Poor Lumi can't catch a break with this guy Youta screwing up as much as he is.
-He pretends not to understand why she gets upset whenever he unnecessarily throws himself at other girls
-Is usually hardhearted toward her, outside the context of sex
-He has never responded to Lumi's declarations of love--any of them
-He almost completely or completely forgets her the moment another girl enters the picture
As much as this guy has some traits that your average harem MC doesn't, the above remind me of those that said average MC absolutely do: a mixture of donkan and callousness. At least he has his moments in which he remembers Lumi or shows concern for her.
What follows is a guess; it might be a spoiler, so read at your own risk.
That aside, the way that thing that keeps defenestrating him looks has been bugging me--I now know what it reminds me of: it looks like a monstrous teru teru bouzu. And it makes sense: he himself said that he's called "The Sun" by others, and his name is in fact close to "taiyou" (lit., "sun") backwards. That TTB is actually a prayer for the "sun", Youta, to come out. Whose prayer that TTB is, though, is something I don't know.
I was not expecting some decent story telling from a Harem Isekai.
As for Nishina...what ars the chances that she's the Jealous God. What if her dying sent her 3 thousand years into the past, or if some event will send her to the past to become the Jealous God.