Have you guys never thought of like Yotsuba dressing up as Itsuki and kissing Fuu-kun in the anime( I haven't read the manga yet but im planning to i just dont know where to read it lol) cause like the sisters dressed as Itsuki for their Grandpa, knowing that Yostuba is the only one that can run fast, Im guessing its really Yotsuba that Fuu-kun will marry. They might have just showed that Itsuki was the one that got married to Fuu-kun but maybe just maybe they showed us that so that we would think that its Itsuki but its actually Yotsuba.
(Idk if anyone thought of this lol cause this "theory" of mine couldnt let me sleep so I just had to say it here so that I would also know if people agree with me or if they thought if it also. Lol)