At first I thought this was a Yu-Gi-Oh! reference, but after they said water deck and showed the back of the cards it became quite obvious it being the Pokemon Trading Card Game reference.
the brother will get himeno's sister later guys don't worry
edit: I realized I kinda worded that wrong. the newest chapter shows that himeno's sister considers the brother to be "interesting" (because of something he's doing in that chapter). They haven't hooked up or anything, if that's what y'all expecting
@givemersspls Just because your comment was the best of the ones sharing that view. Nothing personal. And yes, your opinion is as good as mine, as long as the author doesn't elaborate. If in a later chapter the big brother turns unequivocally creepy, it naturally will mean you (and the others), were correct beyond doubt. But if he doesn't, I'll keep thinking he was just, basically, complimenting his little brother's social skills and charm.
Am I only who thinks the aniki is pretty cool even tho he looks like a dork? I hope he also gets to continue the family line.
And where exactly is he sexualizing them??? I guess I shouldn't hv called my cousin's 9 y.o kid "a beauty" cuz it apparently meant I was viewing her in a carnal way. /s