Wataru Minakami is sent away from home to Promised Island to attend high school there. He falls off the ferry and almost drowns, but he's saved by a girl who calls him "Big Brother!"

As Wataru gets used to life in the mansion, many mysteries await him. There's a blistering-hot kimchi gratin no one remembers cooking. Then, he encounters a monster out in the woods! And finally... he meets even more sisters of his!

Wataru goes to school for the first time. During class, he fends off all his sisters vying for his attention... and has to do the same thing again at home! Tired of it all, he attempts to escape from the island.

Hinako, the youngest of the sisters, is missing! She left a note that she's "going to look for Mr. Teddy Bear." Kaho asks Wataru to go look for her, and it ends up being quite an adventure for them both.

Hinako sees Wataru using his PC and decides she wants to send him an E-mail. All his other sisters join in, sending him updates on what's going on in their lives. But who is his mysterious pen pal, "Aiko?"

The wind blows a sheet onto Sakuya, and Hinako tells her she looks like a bride. One thing leads to another, and all of Wataru's sisters end up making wedding dresses and staging an entire wedding with him.

Wataru goes to a bookstore, and the shy, frail Maria and her loyal dog Michael accompany him. They have a pleasant time in town together... but then the rain starts pouring and Maria falls ill!

Summer has arrived at last! Wataru and the girls enjoy cold somen noodles, try on new swimsuits, and finally play in the mansion's pool.

The bright summer days continue, and Wataru decides to learn how to swim. The athletic Mamoru takes the lead in teaching him. Can he overcome his lack of talent?

The family goes on a trip, which turns out to be on Rin Rin's submarine! Wataru has a great time with all of them, but then disaster strikes...

Wataru, his sisters, and Mami are stranded on a desert island! They fashion new clothes and continue enjoying themselves. But the island has a secret!

While writing a letter to his friend Akio, Wataru reminisces about his summer vacation and the time he spent with each one of his sisters.

Wataru goes shopping in town with Karen. They have a pleasant day, but then Karen gets lost in the rain while trying to reunite two kittens! Can Wataru find her again?

Aria's ribbon gets blown away by the wind, and she goes to look for it in town, accompanied by a mysterious old man. Then Wataru goes to look for her as well when he notices her missing.

Kaho, the cheerleader, is excited to cheer for her brother at the sports festival. But she gets depressed at her own clumsiness. Wataru will have to give her courage!

While in town with Haruka, Wataru has an escalator accident and sprains his ankle! Will this interfere with their dream of going to the dance together?

Wataru has a strange dream, and wakes up as an invisible ghost! Can the occultist among his sisters, Chikage, return him to his body... or is she the one behind this?

Shirayuki brings Wataru a boxed lunch at school. Then she cooks more and more, until Wataru's stuffed full! He'll have to find a way to turn down her meals without hurting her feelings.

Christmas is coming! Everyone has fun decorating the mansion and choosing presents. Wataru's holy night with his sisters will be truly magical.

Rin Rin builds a mechanical copy of herself to help take care of Wataru, but Mecha Rin Rin keeps breaking down. Wataru gives her what help and reassurance he can.

All sorts of things are going missing around the mansion! Yotsuba, girl detective, is determined to find the culprit. But what if it's one of them?

Wataru's old friend Akio comes to visit Promised Island! All his sisters are excited to meet their guest. Except for Mami...

Wataru finally has the chance to return to Tokyo, but he struggles with the decision. One by one, his sisters find out that he might leave...

The sisters try to get used to life without Wataru. And back in Tokyo, Wataru tries to get used to life without them...

After being challenged by Mami, Wataru makes his decision. He returns to live happily with his sisters once again.