Aquarium.

This is the summer story of Aqua - a beginning maid carrying a secret - and her master (the player) who lost part of his memory.

The young Master, heir to the Francois family, has the same nightmare every night.

In it, he meets a girl, but they always end up quarreling and parting ways with the words "I hate you" ringing in his ears.

But just who is this girl...?

One summer's day, the young Master's elder sister tells him that in order to prepare for succeeding to the Francois family estate, he is to practice his leadership abilities.

To do that, his sister wishes for him to take a new maid under his wing so that he can guide and help her grow.

"I am the new maid, Aqua. From today, I will be responsible for your well-being, Master."

The young Master immediately finds his heart drawn to Aqua, the new, clumsy maid who is burdened by a certain "secret" she cannot speak of. However, the two are separated from one another by an insurmountable wall—their social strata.

What shadow looms over the two as they face challenges and the opposition of society itself?

This is the pure summer love story of two individuals from completely different walks of life.