Mainstay

ARC MainstayMainstay (中堅) arc is the seventh arc of Oshi no Ko manga series. It covers Ruby Hoshino as she began making her way on the entertainment world through featuring at a web variety show that her twin brother is starring, and later on, follows Aqua Hoshino as he discover the hidden secrets of both his sister, and the continuing mystery of their father.

Dig Deep! One Chance
Six months passed since the trip to Miyazaki. The careers of Aqua Hoshino and Akane Kurokawa moves forward, as they both land acting jobs as supporting characters in a drama and headlining a drama respectively. After their music video became viral, B-Komachi's popularity also began to grow. But internally, members of B-Komachi are distant from each other. Kana Arima is struggling to reconcile the fact that Aqua is actually dating Akane, and he even started to deliberately avoid meeting her. Mem-Cho, who noticed Kana's mood one day, manage to dig the truth out of her and confronts Aqua herself. She, however, is met with the fact that Aqua doesn't like avoiding Kana, but has to do it in order for her career to grow, and to avoid another case like her mother, Ai Hoshino.

Meanwhile, Ruby Hoshino has been meeting with the previous president of Ichigo Production, Inc, Ichigo Saitou, and drilled him regarding her and Aqua's father. He refuses to divulge the information, but said that he will arrange a meeting with people that might know about the information if she gets popular enough. Ruby follows his advice and got a job as a reporter on the show "Dig Deep! One Chance", coincidentally the show that Aqua is also starring. She also become closer with the Assistant Director of the show, Shun Yoshizumi.

At one point, Shun is asked to search for cosplayers to feature on the show's segment. He has difficulty finding any cosplayer that can fit the bill, and his distress was not gone unnoticed by Ruby. Shun asks her for help in filling in one of the cosplayer's slot, and so she began asking Minami Kotobuki to join as she has expressed interest in the show before. Meanwhile, Shun asks his younger sister, Mimi Yoshizumi, to fill the slot as she is also a cosplayer alongside her main job as a VTuber.

The day before the filming started, Ruby bring up a significant problem regarding the show's Tokyo Blade cosplay segment to Shun, resulting with a last minute notice for all cosplayers invited to the show. The filming for cosplayers segment begins as Ruby also invited another cosplayer that she knew from a previous job, Meiya. During the shoot, Meiya were asked inappropriate questions by Director Urushibara, and later on, after the filming is over, she writes a tweet expressing her displeasure over the whole experience.

The tweet make waves on the Internet and makes the show unpopular, forcing Director Urushibara to step down as director. Ruby, however, offer a proposal for a special episode of "Dig Deep! One Chance" in order to clear things up with Meiya, involving interviews with Abiko Samejima, and Director Urushibara apologizing directly to Meiya while wearing a self-made cosplay outfit of his favorite character from Tokyo Blade, Sayahime. In the end, Meiya agrees to delete her tweet.

After the special episode filming, Aqua confronts Ruby, suspecting that the scandal was engineered by her. She admits on purposefully inviting loose-lipped person such as Meiya to the already troubled production crew, with the end goal of having Director Urushibara give her a spotlight on the show in order to bolster her popularity. Aqua argued about the morality of her actions to no avail, as she declared that Ai Hoshino is also a liar, and that she will be famous soon.

Going Astray
Six more months passed since the airing of the special episode. Ruby is now a famous celebrity, winning a "Newcomer Award", and her own popularity boosted B-Komachi's YouTube subscribers, but she also outshines her fellow members as a result. Shun Yoshizumi becomes her manager, quitting his job as Assistant Director. Ruby declares her intention for B-Komachi to perform at the Tokyo Dome, in order to fulfill Ai's dream. After a talk with Miyako Saitou, Aqua realizes that Ichigo is behind Ruby's success, and talks to him.

Ichigo reveals that he did not return to Ichigo Production, Inc because he is planning to kill the person that leaked Ai's address to the stalker that killed her. Aqua tries to convince Ichigo that the perpetrator, Seijuurou Uehara, has died, but Ichigo reveals that Uehara was already dead before Ai was killed, therefore making it chronologically impossible for him to be the culprit. Reeling from the fact that his father is alive, Aqua unknowingly knocked down Kana Arima as she tries to give him an umbrella, and she runs away from him thinking that Aqua hates her deeply.

Meanwhile, Akane Kurokawa is attending the Japan Film Awards, and wins the "New Actor Award". She asks Aqua to join her in the red carpet, but he refuses due to his earlier distress. She received many congratulatory flowers, one of them is a bundle of white roses, and notices someone that looks similar to Aqua. During the after party, Toshirou Kindaichi reveals that the sender for the white roses are a former theater actor from Lala Lai Theatrical Company who now owns a production company. She watches an old archive footage for the former actor, Hikaru Kamiki, and deduced that he is Aqua and Ruby's biological father.

Resolving to not let Aqua find out about this, Akane decides to investigate Hikaru by herself, asking around for information. One day, as she walks across the overhead bridge, she was pushed down by a stranger accidentally, but Aqua arrived just in time to save her. Her relief at Aqua's appearance soon turn into suspicion as Aqua begs Akane not to do anything dangerous, and she deduced and finds out the tracker that Aqua has put on her personal item. They have an argument about their relationship, with Aqua firmly denying Akane's request to be involved with his revenge, and breaks up with her.

Aqua deduced his father's true identity from Akane's movements, and plans his revenge. On the other hand, it is revealed that Mimi Yoshizumi's career as a VTuber ended after clips of her real self swearing and insulting people leaked out. Hearing the news from Shun, Ruby talks about the possibility of having Mimi as a new member of B-Komachi, and Kana overhears the conversation. Kana decides to begin exploring her avenues outside of B-Komachi, and meet up with an influential director in a shady place.

Characters Introduced

 * Shun Yoshizumi
 * Mimi Yoshizumi
 * Tetsu Urushibara
 * Meiya
 * Hikaru Kamiki (name reveal)
 * Itano