ข้อมูลอนิเมะKiss x Sis

Keita injures his hand at school and Ako and Riko compete to help him out.

At Christmas, Keita, Ako and Riko go to a karaoke bar where they all end up getting very drunk due to a mistake by the staff.

While searching through Keita's room, Ako and Riko find a dirty magazine featuring siblings in a threesome. Wondering if they may end up doing the same thing with Keita, they have a 'practice threesome' with each other while using a dummy to represent Keita.

The sibling's parents give Keita tickets to a hot spring resort as a graduation gift and suggest that he take the girls along on the trip. The siblings go to the hot spring resort, end up visiting an erotic museum, and find themselves in some compromising situations involving Ako's unintentional purchase of alcohol.

Ako and Riko see their parents kissing at the front door, and hear their mother say, "When you come back, you can have all the fun you want." That evening while studying together, Keita, Ako, and Riko, try to block out the sounds of ecstasy coming from their parents' bedroom, and end up in a compromising position in the process. After becoming so aroused by the sounds their parents' (which, as it turns out, they misinterpreted), Ako, Riko, and Keita cannot get to sleep that night, which leads to further intimacy.

As the school takes a fitness exam, Ako and Riko compete with each other for the best results. Meanwhile, Keita gets into all sorts of trouble trying to keep the other boys from spying on the girls.

As Keita gets soaked on a rainy day, Mikazuki invites him to her house, where he ends up having to hide from Yūzuki when she suddenly comes to visit.

Yuuzuki visits Keita's home for a school visit, where their luck runs true to form and something embarrassing happens. Fortunately for Yūzuki both of Keita's parents are very open minded - maybe a little too open minded.

Whilst Riko is away, Keita develops a taste for licking Ako's sweat. Later that night, Riko makes her own moves on Keita, only to also end up on the receiving end of his newly awakened fetish.