If you pay careful attention, you’ll notice that even amongst the quintuplets their breast sizes vary. Surprisingly, the largest quintuplet chest actually overwhelmingly goes to Nino, followed closely by what is almost a tie between Miku and Itsuki. Perhaps this is owed to seniority, but this doesn’t explain why Ichika’s chest is 4th ranked amongst the sisters. Perhaps this is because as the eldest sister, she has been responsibly been giving nutritions meant for her to the younger ones, as a way of being the responsible onee chan we know she is, thus decreasing her breast size growth compared to most of her juniors.
This is when we realize that while Miku may be slightly larger than Itsuki at the moment, all the food that Itsuki ate will eventually reach into her chest, and soon Itsuki may surpass even Nino when it comes to chest size, which is extremely impressive considering Itsuki is the youngest sister and by virtue of age should actually have the smallest chest. This also explains why Yotsuba has the smallest chest; though by no means unimpressive, one must remember that Yotsuba runs and does the most physical activity, which in consequence burns a lot of fat and ends up decreasing Yotsuba’s chest size to even smaller than expected as the 4th sister.
We must carefully observe Itsuki’s growth; there is much potential in all the food that she eats as like any blessed manga heroine, all the fat goes to her chest rather than to her stomach.
tl;dr: Itsuki’s overeating is a tactical ploy to surpass her sisters in the Futabowl.
