Yori and Iku Yuki are twin brother and sister who have been extremely close all their lives. However, when they are fifteen, Iku notices that Yori has been distancing himself from her, as if he hates her. However, it turns out that Yori is deeply and hopelessly in love with Iku, his own twin sister. Yori is filled with guilt for his love for her, and even beds her best friend in a unsuccessful attempt to forget her. When he confesses his feelings to her, she is shocked and is reluctant to return his feelings because they are, after all, brother and sister. However, Iku eventually realizes that she indeed loves Yori, and together, they embark on a relatiosnhip, even though they are fully aware of the consequences of their actions and have to keep it a secret from their parents and every other person they know.


Yori Yuki:

The male lead character. He is Iku's older twin borther. Yori is very intelligent and the smartest student of his junior high school. He appears cold and intimidating, but he is actually very nice and shy, especially with Iku. He is very protective of Iku, to the point that he prevents other boys from getting too close to her and beating up anyone who makes fun of her. Ever since they were very young, he has been very close with her and even said that he will marry Iku one day when they were small. However, as they become teenagers, he begins to fall in love with his sister and tries to surpass his feelings by isolating himself from her and sleeping with Kusunoki. Once they confess their feelings to each other, they begin a relationship, which they must keep a secret from their parents and friends. As happy as he is being with Iku, he still feels guilty for dragging her over the taboo line of their relationship and is willing to suffer the consequences for her. Near the end of the series, it turns out that he and Iku are half-twins and have different fathers: Yori was fathered by his father's best friend who raped his mother. Then, Yori decides to leave Iku so their feelings can fade within time. 10 years later, Yori is in England and almost doesn't reconize Iku before embracing her and admitting to himself that he still loves her.

Iku Yuki:

The female lead character. She is Yori's younger twin sister. Unlike Yori, she is clumsy, naive, and does poorly in school. While she is jealous of Yori's intelligence and excellent skills, she cares deeply for him and would do anything to keep him close by her. She is a very cute and charming girl who always has on a smile and an innocent personality. She has been close to Yori since childhood and loves him deeply. However, she is oblivious of his love for her at first. When he confesses, she is shocked and is scared to return his love due to them being siblings. Upon learning of his affair with Kusunoki, she is jealous and admitts that she loves Yori as a man. They begin a romantic and sexual relationship, which they keep a secret. Iku is completely content with their taboo relationship, but knows how wrong it is. Near the end of the series, she finds out that she and Yori are half-twins due to them having different fathers. Once their parents discover their relationship and Yori leaves secretly to break of their relationship, Iku refuses to be seperated from Yori and vows to look for him. 10 years later, she is working for Yano's company and travels to england, where she reunites with Yori.

Haruka Yano:

Yori's best friend from junior high school. Like Yori, he is intelligent and has a serious-looking appearance. He and Yori are very popular in school, but both ignore the attention and see it as annoying. Yano knows of Yori and Iku's incestuous relationship, as Yori later confesses it to him during graduation. He keeps their relationship a secret and lies about it to other people who grow suspicious of the twins' closeness. When Yori moves out of town to attend high school and Yano tends to Iku, he begins to fall in love with her. He even threatened to steal her away from Yori. He later finds out that the twins' may be not fully related since they have different birthdays and of their mother keeping a secret. By the end of the series, he confesses his feelings to Iku, but she rejects him and proclaims Yori as the one she loves.

Tomoka Kusunoki:

Iku's former junior high school best friend. She has always had a crush on Yori due to his good looks and hung out with Iku mainly to see him. While tending to Yori's injuries after a fight, she confesses her feelings to him and asks if she is good enough for him. This leads to him seducing her in order to forget his feelings for Iku. She takes this as him being her boyfriend, however, he later rejects her and says that he is in love with someone else, leaving her shocked and heartbroken. She eventually discovers Yori and Iku's incestuous relationship and threatens to expose them to their parents as revenge on them both. However, Yori overrides her plot by destroying her evidence against them and threatening her to leave them both alone.

Yori and Iku's Parents:

Yori and Iku's parents are very doting and loving towards the twins. Near the end of the series, it turns out that they had been childhood sweethearts and decided to marry after college. However, their mother was raped by their father's best friend on the day of the wedding and slept with her husband to forget the rape. 3 months later, she finds out she's pregnant with twins and was unsure of who was the father until they were born and realized Iku was fathered by her husband and Yori was fathered by her husband's best friend. This was kept a secret for 16 years. Their mother walks in on the twins making love, suffers from shock, and confesses the truth of their parentages. By the end, before Yori leaves, the twins come clean about their relationship and their parents decide to forgive them, due to the fact their mother had kept a secret from them.

Manga Information


Boku wa Imouto ni Koi o Suru

Alternate Title

I Love My Younger Sister


Kotomi Aoki





May 2003 – August 2005





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