I remember reading somewhere that Umi has the same age as Maki but they still are senpai-kouhai, is it true?
Well, Umi was born in March and Maki in April, so I think they are actually only a month apart. Because of when Japanese school years start and end though, they ended up in different years, I think. Umi is one of the youngest in her year, and Maki is one of the oldest in hers, unless I'm missing something.