|Release Date||July 24, 2007|
Purity (無垢,Muku) is the fourth episode of School Days anime.
Reading in her bedroom, Kotonoha is interrupted by Kokoro. She asks Kotonoha with help with homework but happens to spot the books Kotonoha is reading, only to stop when she realizes she can't understand them. Kotonoha tells her they are romance novels, and Kokoro keeps asking her about her own time with Makoto and asks if they kissed. Kotonoha is surprised by this, but eventually tells her that it has nothing to do with her. Kokoro starts to tease her, thinking they have kissed and this annoys Kotonoha.At School, Mokoto continues to complain to Sekai about the ordeal of having a girlfriend. He tries to explain but struggles. As she goes to hang out with her friends, Sekai recalls her own kiss with Makoto at the station on that day.
Meanwhile, Makoto and Kotonoha make out on the roof top, only to be stopped when he tries to fondle her breast. She tells him that she isn't mentally prepared for it, then leaves, claiming she has errands to do, leaving him dismayed.
At Kotonoha's house she chats about it to Sekai. She tells her that she will scold him for doing this again, but Kotonoha starts to feel badly. Sekai tells her not to worry though, and tells her that she is being too considerate for his feelings. She asks if Kotonoha has any plans to do something with him in the future, but changes the subject and they discuss the Horse Riding Club instead.
Meanwhile, Makoto thinks about how he touched Kotonoha earlier.
Sekai mistakes the horse discussion for a sexual position while Kotonoha gets a drink from such a long chat. She spots a ticket nearby and asks her mom if she can use it to invite Makoto to attend an event with her.
While at the Train, Kotonoha prepares to invite Makoto but the train suddenly jerks, causing Makoto to accidentally touch her breast again. She apologizes, but he claims it was his own fault and recalls that she didn't want to be touched. As this goes on, Hikari spots the couple and after reaching school, she quickly tells Sekai about the romance between Makoto and Kotonoha. They grow awkward before suggesting that Sekai break up with him.
At class, Sekai asks if she is going to have lunch with Kotonoha. She declines as Makoto points out that he will be having lunch in the cafeteria. Sekai plans to join her friends and she is quick to chastise Makoto for doing something that Kotonoha hates. Makoto incidentally gets the attention from the other students when he yells at Sekai and he pulls her out of class and into the hallway. He admits that he wants to go beyond kissing with Kotonoha, but he is unable to. Sekai realizes that he is being honest with is feelings, but tells him that Kotonoha doesn't want to be handled aggressively. She goes on to suggest he tries again at her home, but he is quick to point out her little sister would be there. Then she suggests he try to invite Kotonoha to his place, but he declines again due to having to hide his gravure magazine beforehand. With this, Sekai figures that he should try to do things with Kotonoha's feelings in mind, then offers to let him practice on her. This leaves Makoto very confused.
During class Makoto thinks about Sekai's offer to practice. He asks about it using his notebook to communicate with her again, and she tells him its about a girls feelings.
After class ends, Makoto is prepped by Sekai for the so-called practice. He claims he hasn't given his consent to the idea yet though, only to be interrupted by Taisuke, who still has the love manual that Makoto owns. He asks about the missing page in it and Makoto comments that it was left at home, allowing him to avoid Sekai until she tells him to remember what is more important; starling both him and Taisuke. When Taisuke takes off, he reluctantly agrees.
At the park Sekai finds a place for them to practice but they were interrupted by many kids who mostly found them hidden in the park. Afterwards they stop by at the karaoke box after spending time singing together they begin to continue their practice but realize that there were cameras watching them, frustrating the both of them as they are unable to find a private practice spot. Sekai then resorts to taking him back to the School roof top.
Meanwhile at school, Kotonoha glances at the ticket she had planned to give to Makoto earlier. She reads his apologetic message for not meeting earlier.
At the rooftop Makoto and Sekai start to practice. Sekai pushes him and he realizes what she is intent on doing, but she coerces him by telling him to pretend she is Kotona. She lets Makoto fondle her breast, but as he tries to lay her down on the bench and starts to unbutton her blouse when he gets a text from Kotonoha. He decides to end practice when Sekai is about to leave to attend to her errands. Makoto asks if they can continue to train elsewhere, but she refuses and tells him that he should do the rest on Kotonoha. They part ways and Makoto reunites with Kotonoha at a Convenience Store. They both apologize for the day before and Kotonoha invites him to join her at the pool on Sunday, to which he accepts.