This story is so stupid, it's a SJW socialists wet dream, setting the premise of interbreeding as human erasure, which is true (and spun in the West to erase Whites, featuring mixed couples everywhere in the media).
We have the SJW leftist socialist soyboy friend who calls his "friend" (actually enemy,who he's tormenting with irrational commentary) by anti-white slurs like "racist" for calling out the obvious truth.
We have the non-Japanese horny alien girl who cannot accept the boys agenda and tries to guilt-trip him into accommodating to her wishes.
And we have the main character who has reasonable thoughts and insights, but lets himself be guilt-tripped into submission by a crying, scheming girl and his manipulative "friend".
And yes, the invaders are parasitic, they are like the "DearS", just some millennia ahead in the process of gathering genes and scientific advancement from other species that worked hard to achieve what they had.
It's uncannily showcasing how terrifying the prospect of getting erased is, the public morals and achievements dwindle away while trying to accommodate to the foreign entities, people in power creep up their arses and persecute their own citizens for daring to note the underlying threat of erasure, and "inclusion" and "tolerance", a societies greatest weakness and an indicator for its upcoming demise, are spread as new "virtues", replacing true virtues and culture till the invasive entities have completely taken over.
Ethnicity is the single-most uniting factor in a society, since different ethnics actually never really mix, and in the end one is erased in favor of the other. Having several ethnics in one nation will divide the nation and in the end collapse it, unless it's terrorized by a common religious and political ideology.
This manga is one of the greatest examples as to why it is important to stay biologically homogeneous, keeping your ethnostate healthy and future-proof. Japan and Europe have to stop taking a knee to anti-White bull$#!+ and start going free, into a future where the prosperity and safety of their own indigenous people matters the most and where immigration of non-indigenous people is abolished.