Akaya Kodai is the Commander of the mercenary unit Venus, and the sole male member. He is a former member of the Maken-ki student group, before it became an all-girls academy. While Venus stays at Tenbi, Akaya challenges Takeru's viewpoint of wanting to protect all girls when he asks Takeru what he would do if a girl were to do bad things to another person. He is the primary antagonist for the Venus arc.
While Akaya was still at Tenbi, he led a group of Tenbi students to assault a female student years back, which results in the school's changing to all-girls, and also kills Takeru's mother. However, it turns out that these were just false memories implanted by Ouken Yamato in his mind and the "victim's", in order to blackmail Tenbi into having Gen work for the Kamigami. Akaya, after learning the truth, volunteers himself in place of Gen, saying that he will create a world class team within a year, and in exchange the Kamigami have to leave Gen alone. This is why Venus was created.
Swindle - a revolver with 6 bullets, where each bullet has a different ability, or Trick. The known Tricks are:
- Illusion - Akaya's target sees illusionary copies of Akaya, as well as concealing the real one from their vision.
- Vision - Akaya projects a large screen in midair which shows himself. He can use this a broadcasting system.
- Hypnosis - Akaya's target either falls asleep or listens to whatever Akaya tells them.
- Dummy - Creates a perfect double of Akaya, with all his powers and abilities. There is no one who is able to discern which is the real Akaya.
- Dual - the Hidden Gun.
Akaya arrives at Tenbi with the rest of Venus in a helicopter, and are seen by Gen who is giving Takeru his Maken. Akaya appears at Minori's door, spouting romentic lines about how long its been and how beautiful she is, only to get the door slammed on him. He tells her that members of Venus are her new exchange students, and claims that he has orders to investigate rumors of a potential plot to revive Yamata no Orochi, to which Minori bursts out laughing. Akaya points out that the spirit source of Tenbi, Amanohara, has had a large increase in Element, and tells her Kamigari believes that someone is weakening the seal around the creature. At this point, Gen bursts in with Aki and Tomika and demands to know what Akaya is doing at Tenbi, to which Akaya mostly ignores and simply tells him that he's a substitute teacher. As Takeru, Haruko and Furan arrive at Minori's office, Akaya charms Furan and asks her to lead himself and Venus to the Maken-ki room.
Akaya next shows up at the match between Maken-ki and Venus, and comments on the fact that both sides are enjoying the match so much because they are surrounded by people just as powerful as themselves, while still being able to go head-to-head with them. As he stands next to her, Aki asks him if he will tell her why he's at Tenbi, or if she has to figure it out herself, but he makes no response.
[Note: In the manga, the dispute between Azuki and Yan Min is settled by a hockey game in the empty pool, instead of a volleyball game as seen in the anime. Akaya shows up in a swim briefs, which shocks Furan a little, to watch the game, and comments that Yuka's innocent game is quite cunning, as neither are likely to win due to the game's rules.]
Akaya turns out to be the teacher for home economics, where the female students fight to try and impress him with their cooking, each trying to get him to sample their food before the others.
He is selected as the male teacher for the cavalry competition between the boys and girls, and steals Azuki's headband from her by jumping and performing a one-armed handstand on her shoulder, before jumping back to his own team. He also managed to get Aki's headband, but Minori's irritation at his posing leads to her slamming him into the water, taking him out of the competition. In the manga, Akaya and Aki are tie by taking each other's headbands.
Later, in a fight with Takeru, he reveals his 'past' in order to destabilize Takeru's emotions and have him release his ultimate powers. When Takeru attacks him with Blood Pointer, he notes that incomplete describes Takeru's power perfectly, but that it was still so beautiful. He then shoots Takeru through the heart, which leads to Kodama unleashing her maken and attempting to destroy him. He later says that the fight was mainly to test Maken-Ki's strength to report it to the Kamigami. He is then slapped by Aki, who yells while crying at him that she hates the lies he makes up, and that he's pretending to be the villain to feel better about himself.
When Venus is leaving Tenbi, Akaya is confronted by Takeru, who has learnt that Akaya's "past" was a lie. However, he still has no forgiveness for Akaya, attempting to punch him. When Takeru starts beating himself up for his weakness, Akaya mentally comments that what he really wanted to see what not how strong they were, but how strong Takeru's emotions were, and whether that emotion would overcome Akaya's determination. He then tells Takeru that they are similar, in that Tenbi is precious to both of them and they would do anything to protect it. Takeru counters that he thinks Akaya's methods are wrong, to which Akaya challenges him to become strong enough to defeat him.