Colorful Aquarium

Our hero has spent a long time living alone with his elder sister while their parents were away on business. However, now the sister has gone and the protagonist has been living alone for a little while; living the student’s life. At least he has had other company than just his sister, for he was frequently visited by his childhood friend. She now is kind enough to offer to live with him, and help him with the chores and such. To make things even more interesting: a girl--that both of them knew from long ago--has now returned from America along with two maids. The three of you hit it off very well together--so well that it leads to something more than a friendship between all of you.