The following article contains spoilers for Oshi no Ko. The latest chapter is available on Manga Plus. The anime adaptation is currently streaming on HIDIVE.
Every anime season, the "best girl" argument always comes up. In some cases, there is a distinct bias on the production's part, but for Oshi no Ko, the entire female cast are made up of exceptionally written women. The eccentric Kana, for her drive and motivation to succeed; the excitable Ruby, with a passion for the arts; the funny and quirky Memcho, who's always there to support her peers; the motherly Miyako, who mentored the Hoshino siblings; and the perceptive Akane, the mature and vigilant actress.
For our main character, Aqua however, there may only be one who's a better match for his love life; let alone one who can deal with the "true" him.
Wordplay and Mind Games
Something unique about Akane's character, is her ability to read people and piece things together with what limited knowledge she has. This could be attributed to the fact that she was initially very shy at first, and so she likely just quietly observed those around her. Moreover, during her research of Ai, Akane could tell that not only was Ai hiding something, but at some point during her career she had a lover and possibly became pregnant, which would explain her 9 month-long hiatus. She also has a logical mindset - such as when Aqua confided in her about him not needing revenge anymore, when he believed his "father" had already died. However, she quickly noticed the inconsistency in his story, and deducted that based on his strained behavior prior, his feelings prevented him from seeing that his real father was still alive, due to his subconscious desire to find happiness. Akane is also very much aware of Aqua's tendencies and has no trouble reading him - even if she can't always predict what he plans to do next.
The Middle (Wo)man
Akane is able to place herself in a neutral position and see both sides of the story. While she intended to kill Hikaru, Aqua's father, so the latter wouldn't take the blame for it, she also recognized that Ai likely didn't harbor any resentment toward her killer, as stated in chapter 116. Aqua and Ruby, however are driven with grief and resentment, so they can only focus on what was taken from them. Because of this revelation on Akane's part, she finds the resolve to stop Aqua from destroying himself. Someone who truly cares about you, will not enable every decision you make, but rather try to prevent you from making the wrong choice. Her empathy allows her see the situation for what it is. There are no winners when it comes to revenge.
Mutual Maturity
Akane is still young, and so she can be naive at times, but as stated previously, she acts logically and is calculating herself. This also plays a part in how she acts on stage. "Methodical acting" is when an actor researches and puts themselves in their role prior to their performance. This allows them to understand and effectively portray the characters they act as - it can especially be helpful with improvisation during filming. Aqua uses a similar technique, as he reads the intentions of those around him and mimics their behavior to get on their good sides. Though it's precisely because of their similarities in acting, that this causes a strain in their relationship.
Raw Emotion
Aqua initially uses Akane as a means to learn more about the acting school she went to, given that presumably that's where Ai met his father. But after he declares his vengeance no longer necessary, he resolves to stay with Akane and nurture their relationship further. She's also the only character he opens up to and confides in about his feelings. Ironically before being temporarily "free", Aqua was the one who listened to and comforted Akane - but when before and during his "relapse", he confided in her. This makes for an equal relationship; though Aqua's trust issues led to a breakup. Looking at both of their characters, there's a mutual effort being put in. Akane, having no burden to bear can give it her all, but Aqua struggles despite wanting to trust again - and so makes the decision to break it off, so she doesn't get dragged into his drama.
As of right now, we can agree that Aqua isn't in a good place to be in a relationship, anyway. But if he decides to come around, we know Akane will be there to support him.