"Sexy Onee-sans" (and FAKKU Subscribers who are into OneeShota stuff) Win; Flawless Victory ... LOVE-Tality!
Looks like Aki-kun has become both a Man Of Culture and a Lucky Bastard (GRR) at such a relatively young age - pause to salute with manly tears. And it also seems the sisters' mother has *koff-koff* given her Approval for the three of them to be together; perhaps deep down, "A Mother Knows (say-no-more, say-no-more)."
Ooh, an afterstory sequel!
"They're treating me really well"? Yeah...I'd say.
What a nice ending. So he is basically a mediator that helped better their relationship together as well...And I'm sure all 3 of them will continue to get along just fine from now on.