Conspiracy theory: Ichika is being underhanded mostly for Miku's sake. She does love Fuu-kun and it shows but her intention most of the time is to put Miku farther ahead than anyone else. She was dressing up like Miku to make her look good in front of Fuu-kun but keeps getting caught every time.
Also: Youtsuba was the original Rena that first met and had shenanigans with Fuu-kun but each of the other sisters also spent some time with him later. The last part was confirmed somewhere where Ichika was reminded by Youtsuba how she stole a "friend" she was hanging out with. Furthermore, Youtsuba actually has loved Fuu-kun since day one but because of her guilt behind making everyone fail along with her she suppresses her feelings, knowing they all love the Fuu. Fat Quint is just playing pretend.