Aki

because of the disappearance of Masamune, in which she told him that she gorged it off on food and felt miserable ever since. Since she is called the Cruel Princess, if anything embarrassing was to come out of the school that revolves around her (such as her habit of eating too much) Aki's image of being the cruel princess would be tarnished. This is one of the reasons why she eats in the storage room, another is that if she was eating a normal amount of lunch, her stomach would rumble loudly af