Sanou Tsushima (対馬 左脳, Tsushima Sanou) is a junior of Class 13, though he is not a member of the Thirteen Party. Instead, he and his twin brother Unou Tsushima were the guardians of the Door of Rejection.
Despite being the "Normals" of the Abnormals, the twins are both still very arrogant, and are supremely confident in the superiority of Abnormals. They are very close as twins, often speaking off of one another. They are consistently shocked by the feats of the Student Council against the Thirteen Party as they follow them through the underground facility of the Flask Plan. Sanou's lucky color is black.
Sanou is nearly identical to his twin in appearance, except that his hair is black, and his bangs hang over his gray right eye. He also wears a black uniform with a white trim as opposed to Unou.
Thirteen Party Arc
Sanou and Unou are waiting for Medaka Kurokami and Zenkichi Hitoyoshi when they arrive at the Door of Rejection. The twins inform them about the rules of the door, and are shocked when Medaka manages to get through. They regain their composure afterwards though, and smugly inform Zenkichi that there is no way he can pass through. They maintain this attitude when Kouki Akune and Mogana Kikaijima show up, only to be stunned once more when Kikaijima passes through. They are horrified when Akune makes clear his intent to simply break the door down. After Akune has successfully destroyed the Door of Rejection, the twins can only stare. The Student Council comes to another door, which the Tsushima twins identify as an elevator. However, Medaka chooses to forego the elevator in favor of the stairs, a choice that surprises Sanou and his brother. When Medaka points out that the group is lost, the twins reveal that the first floor is actually a maze. They both express their outrage when Zenkichi asks them why they are tagging along, stating that they have no job anymore now that the door they were guarding has been destroyed. After Kikaijima's scream, Sanou and Unou explain that she used sonar along with Medaka to uncover the layout of the maze.
The twins watch on as Shigusa Takachiho confronts Medaka. Both are horrified to see Medaka shrug off Takachiho's kick. They continue to watch as Medaka is knocked down by Takachiho. Seeing Takachiho in action, that remark that he is totally different from them. Seeing Medaka use Myouri Unzen's super balls, they wonder if Takachiho will be able to dodge. The twins are both morbidly amused when Takachiho breaks Medaka's arm. They are shocked however, when they see she sacrificed her arm to steal Takachiho's flash drive. The twins are stunned when they hear that Medaka has no reflexes. They are surprised when Zenkichi orders them to back up. Sanou and his brother are amazed by Medaka's Kurokami Phantom. The two can only stand in awe of Medaka's abilities after seeing the damage Kurokami Phantom did to her body as well.  When Akune remarks that even Takachiho isn't dodging when he and Medaka begin trading blows, the Tsushima twins point out that, in his exhausted state, Takachiho is unable to dodge, as his muscles are unable to keep up with his reflexes. They express their disappointment that a member of the Thirteen Party would get into such a state, and declare that the battle is Medaka's. Sanou is visibly unsettled when Takachiho starts laughing. They are amazed when Takachiho manages to dodge one of Medaka's hits.
The Tsushima twins arrive on the second floor with the Student Council. They are shocked to find Kei Munakata there. After Munakata introduces himself, they reveal that he is on the nation's most wanted list, explaining his abnormal desire to kill people. The Tsushima twins are amazed as Zenkichi successfully deflects Munakata's multiple swords. They are stunned when Munakata reveals a spiked staff. They are further stunned when Zenkichi stops the weapon with his shirt. When Munakata pulls out a rocket launcher, the twins are shocked. The Tsushima twins arrive on the second floor with the Student Council. They are shocked to find Kei Munakata there. After Munakata introduces himself, they reveal that he is on the nation's most wanted list, explaining his abnormal desire to kill people. The Tsushima twins are amazed as Zenkichi successfully deflects Munakata's multiple swords. They are stunned when Munakata reveals a spiked staff. They are further stunned when Zenkichi stops the weapon with his shirt. When Munakata pulls out a rocket launcher, the twins are shocked. The Tsushima twins stand aside as Munakata declares that Maguro Kurokami is responsible for Zenkichi's death. They watch on as Medaka repeats Zenkichi's name. They are surprised at the strength of Zenkichi's stomp. They stand by after Munakata is defeated. After hearing Zenkichi's declaration that Munakata is no killer, Sanou questions if Munakata was faking his Abnormality.
The Tsushima twins follow the Student Council down to the third floor. They are shocked when Medaka and Kikaijima begin to fight. While Medaka and Kikaijima form one search group, Sanou and his brother form another with Zenkichi, though they quickly start arguing. The Tsushima twins watch on as Zenkichi and Akune argue. The Tsushima twins are put out when Nekomi Nabeshima suggests they use the elevator. They wait outside the elevator with the rest; Sanou is amazed by the members of the Thirteen Party, asking Munakata and Takachiho if they can solve the limitless password as well. The Tsushima twins are annoyed by Nabeshima's reaction to the Plus Six. The Tsushima twins are shocked when Munakata immediately pulls out his guns and opens fire on the Plus Six. They are even shocked to see the group unharmed, as Shoko Kamimine has caught all the bullets in her mouth. Later, he, along with the Plus Six and the Loser Team, is defeated by Misogi Kumagawa.
Kumagawa Incident Arc
Following the battle, Sanou is sent to the hospital along with the rest of Kumagawa's victims. Instead of external wounds, those who got pierced through with the giant screws took severe mental damage. On August twenty-second, Sanou is among Medaka's former enemies who show up to cheer for her during the President's Battle.
Bouquet Toss To The Future Arc
The Tsushima twins are among the students who confront Medaka at the beginning of the 100 Flowers Run, holding flowers number fifty-eight and fifty-nine. Sanou and the others are all blown away by Medaka's Kurokami Final. All present wonder if Medaka thinks of their time together as good memories. The twins combined message to Medaka is that all the doors are open to her.
Superhuman Physiology: As an Abnormal, Sanou must have some superhuman abilities, though what they are is never shown. Unlike the members of the Thirteen Party, he cannot pass through the Door of Rejection.
Differences Between Anime and Manga
In the manga, the Tsushima twins follow the Student Council into the Flask Plan labs. In the anime, the twins are absent.
- The twins' name translates (loosely) to Two Peas in a Pod, Right Brain, Left Brain.