Akane and Nekomaru quickly develop a strong bond with each other due to their desire to improve themselves physically. As a result of her athletic talent as the Ultimate Gymnast, Nekomaru was quickl to aid her in trainings as a result of him being the Ultimate Team Manager, a person typically training other athletes.
In Chapter 2, the two are shown to train together for the first time. Their training is so intense as a result of their strength that it initially causes a bystander witness, Ibuki Mioda, to panic; believing another murder is about to happen. The two also train together before Akane heads for the girls-only quality time at the beach organized by Sonia Nevermind, with their training being so intense that it caused Akane to arrive covered in blood. Them spending time together prior later proves to be an alibi for Akane for the second case.
A Special Time Event in Chapter 3 reveals that Nekomaru has been doing "it" to Akane - giving massages, which Hajime Hinata and Kazuichi Soda find out upon investigating it after being intigued by how suggestive their conversation about doing "it" sounded. Later, Nekomaru decided to guard the third island's entrance due to being worried that Akane would do something reckless, which she indeed does by challenging Monokuma to a fight. The host attempts to punish her with a shot from a bazooka for breaking the rule against the violence against the headmaster. However, valuying the time they spent together, Nekomaru stands in the way, taking the shot for her and saving her life. Akane end up worrying about Nekomaru's well-being, even outside of her Cowardly Disease. At the end of the chapter, she was also the most shocked to discover that Nekomaru was turned into a robot.
Nekomaru winds up once again saving Akane from being killed by Monokuma at the start of Chapter 4, this time not even getting injured thanks to his robotic body. After the group split into teams to investigate the Funhouse, Fuyuhiko Kuzuryu told Akane to make sure to thank Nekomaru for saving her life while she still can, especially since unlike him she has the opportunity to do so. In spite of usually being strong, both physically and mentally, she was really depressed about his death, also regretting never saying thank you to him for always defending her. After the end of the Class Trial, Akane refuses to listen to Gundham Tanaka's explanations of why he killed Nekomaru, believing he's only trying to justify what he did, until Nagito Komaeda points out Nekomaru must have shared Gundham's beliefs due to agreeing to their battle to death.
Akane's close relationship to Nekomaru led Kazuichi to use some of Nekomaru's remains to create a miniature version of their deceased friend to cheer her up at the start of Chapter 5, a gift which she treasured and kept with herself until the end.
As seen in Despair Arc from Danganronpa 3: The End of Hope's Peak Academy, their relationship at Hope's Peak Academy seemed to be more or less the same as in Danganronpa 2: Goodbye Despair. Akane and Nekomaru would often fight, with Nekomaru considering it training, but Akane considering it battle. The two were rather close despite their constant fighting.
In Episode 1, Nekomaru was the one to catch Akane and thus force her to participate in homeroom class. In Episode 2, they fought together as a part of their training inside their classroom, causing a lot of destruction around. Later in the episode, both were infatuated with each other under the effects of aphrodysiacs. In Episode 8, Akane was confident that Nekomaru, along with Gundham Tanaka, would manage to hold his own against the army of Reserve Course students who intended to beat them up.
The two have two events together in Ultimate Talent Development Plan, the non-canon bonus mode of Danganronpa V3: Killing Harmony. During the sports festival as well as during their winter event, they once again talk about doing "it" together. They also have one more event, which they share with Usami.
- “Akane...Fuyuhiko has finally come back to us. You better not do anything reckless... I can't stand...the thought of losing someone...any longer.”
- — Nekomaru telling Akane not to do anything reckless so he won't lose her, in Chapter 3 of Danganronpa 2.
- “That stupid fool! No...I'm the one who was the fool... It was my mistake to not keep my eyes on her! Tch...! As a team manager, I should've had a proper grasp of my athlete's private life... Dammiiiiiiit! This failure will haunt me for the rest of my life, or my name isn't NEKOMARU NIDAIIIIIIII!!!!”
- — Nekomaru blaming himself for Akane acting recklessly by fighting Monokuma.
- Akane – “N-Nekomaru...Why did you...s-save...?”
- Nekomaru – “Ha... Isn't it obvious...? Supporting their athletes....is...a manager's duty. H-However... Wh-What a shame... For someone like NEKOMARU NIDAI...to... It was just a little shot from a bazooka... I really am the worst... Heh...hehe...hah... Akane... The time I've spent with you...i-it...it wasn't so bad... Don't...die...Akane...”
- — Akane and Nekomaru's dialogue before the latter's first "death".
- “There's no need to worry about worryin'! I know coach Nekomaru is a monstrous guy. There's no way he's gonna die from somethin' like that... There's no doubt! Nekomaru is definitely gonna come back! S-So...when that happens...I'll make sure...I apologize to him. Cause I was too weak, and I caused him trouble... So when he comes back... I'll make sure...to say I'm sorry.”
- — Akane wants to apologize to Nekomaru for nearly getting him killed.
- “When I think about Nekomaru...it's like...my knees start shakin'... That's weird... There's no way...I've got that kinda weakness. It'd prolly go away if I battled a strong dude, but Nekomaru's not here...”
- — Akane about her feelings to Nekomaru.
- “I'm sure you don't want to hear this, since I caused a similar incident... And I already know that a guy like me has no right to say this to you but... But...when I look at you, I just have to say something...! You don't need to act so stubborn, you know? 'Cause...I know what you're going through. The only reason you're standing here right now...is because someone sacrificed himself for you... You feel guilty about that. Isn't that right? So you don't want to be honest about it, huh... Well, I understand that feeling too... But like he said, it's better to just be alive... It might hurt to look at his painful appearance right now... But you're much better off because at least he's still alive! I mean...for me... ... S-Sorry... Right now...I feel very grateful to her... But I can't tell her that anymore. But you're different. So... Make sure you tell him how grateful you are...”
- — Fuyuhiko Kuzuryu giving Akane an advice about Nekomaru in Chapter 4.
- “Why is Nekomaru...? Why did he have to die...again? Dammit... I never paid you back... I never paid you back...for your help last time! WAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAHHHHHHHHHHHHH!”
- — Akane crying after Nekomaru's death.
- “I'm here today...because coach Nekomaru risked his life...to protect me... I'm gonna be the one who avenges him! I'll definitely find out who the killer is!”
- — Akane motivated to avenge Nekomaru's death by finding out his killer.
Akanidai sailed as a result of their canon interactions, with the two often training together. The very suggestive Special Time Event where it was revealed that the "it" that Nekomaru has been doing to Akane were his massages further fueled the ship. The aphrodisiacs scene from the second episode of Despair Arc, where they showed interest in each other, contributed to this even further. The fact that their most important interaction is with each other also helped. So did both times when Akane mourned Nekomaru's death.
Both being the main person they interact with, they're typically the prime choice of shipping for both characters included in the ship. In fact, it's the most popular choice for both, beating the popularity of any other combination for both characters. This can be seen for example on Archive of Our Own, where it is the most written ship for both of them.
Fan fictions tend to portray their relationship the same way the canon did, with them being training partners. Some, however, include an actual romantic relationship between the two. The latter can especially be the case if the fanfic refers to the aforementioned aphrodisiacs scene. Fan arts are similar in this regard, with most showing the two training together, usually in a fierce battle.
- Akane's relationship with Nekomaru on Danganronpa Wiki
- Nekomaru's relationship with Akane on Danganronpa Wiki