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?"

Hoping to win a mysterious prize, the family decides to perform a play together. Wataru naturally ends up in a starring role as the prince. Then he has to decide which sleeping beauty to awaken with a kiss!

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.

Karen and the eleven other sisters are is excited to meet their beloved big brother again! They bustle about town to get ready for his arrival, and mishaps befall them as they do, but Big Brother's understanding knows no bounds.

Kaho prepares a special gift for Big Brother, but it goes missing! Luckily her sister, girl detective Yotsuba, is determined to solve the case. Afterwards, Mamoru remembers how she struggled with her tomboyish nature until Big Brother helped.

Kaho weighs herself, and the results are devastating! She goes on a diet, but it's hard for her as Big Bro and her sisters enjoy sweets together. Afterwards, Aria finds herself in a mysterious, magical mansion...

Kaho's staying over at Big Brother's place, and she buys cute new pajamas with her sisters' help. They have a fun-filled evening together. Afterwards, Hinako goes out in the rain and faces her fiercest enemy yet: a frog!

A strange girl who looks like Chikage gives Big Brother a ticket to the planetarium... then, later, demands it back! It's not easy, but Big Brother solves the mystery. Afterwards, Kaho remembers the pretty red shoes she got long ago.

Big Brother and the sisters go on a camping trip. Mamoru had a gift for Big Brother, but will she get the chance to give it to him? Afterwards, Rin Rin remembers how her grandpa taught her to love inventing things.

Aria spends a day with Big Brother, but she's sad when it ends... so she hatches a plan to make him come back! Afterwards, Chikage prepares a sinister ritual to win Big Brother's love for herself alone.

Big Brother spends the day with Maria, while Karen tries to keep Aria and Hinako occupied to give them some time alone. Afterwards, Yotsuba remembers the time when she first moved from England and met her brother.

Rinrin and Yotsuba get curious about what Big Brother does when he's out alone, and decide to follow him secretly around town. Afterwards, Haruka thinks about her first Tanabata festival together with Big Brother.

Big Brother gets a love letter! Sakuya decides to stick close and protect him from his other admirers, but can she confess her own feelings? Afterwards, Marie has a sweet dream of her brother.

Sakuya is heartbroken when Big Brother doesn't recognize the gift he once gave her. She runs away and wanders the town, awakening her own memories of her time with Big Brother. Afterwards, Shirayuki reminisces about how she learned to bake and make sweets.

Thanks to Sakuya's hard work, the sisters go to a fancy restaurant with Big Brother and have a lovely evening. Afterwards, Sakuya dreams of being Big Brother's bride and getting married in a church.

Big Brother and the sisters get ready for a special Christmas together, but none of them can decide on which present to get for their brother until they have a brilliant idea. Then Big Brother works hard to make sure the Christmas tree is perfect!