And I'm not so certain that Kyusaku and Ryunnosuke
would so easily accept Akiko being controlled by an alien.

I see them not as accepting that Akiko is hosting Darshian so
much as accepting a temporary standoff for the sake of a
long-term solution.  They both want Akiko back, but they know
that the problem is much larger than that, and pushing for quick
gains risks much larger losses.

Oh, I have no problem with them accepting the situation.  I have a
problem with them *easily* accepting the situation.  There's nothing
in the way of objection to the plan.  I can see Ryunnosuke, at least,
objecting violently and perhaps having to be calmed by Kyusaku.

That's maybe heavier than you want to go.  But maybe a few sentences
of resistance, you-better-not-hurt-my-mom kind of stuff, is called
for.

Just my opinion, of course.  Feel free to ignore.  :)

-Richard