I looked into tvtropes for Oshi no Ko out of curiosity and holy shit it is bad. Pure cope for listing the ending as bittersweet. There's nothing sweet about it. Guy sacrificed himself and done massive damage to everyone.
And the twins father was another actor the same age as the mother that was previously raped by a female actress? Holy shit, what a copout after implying she fucked a higher up. It's amazing how a show that alleges it shows the underbelly of entertainment media is hellbent on the mother being a saint.
You're being far too generous to that ending.
Aqua killed himself unnecessarily when they had someone who'd attempted murder on his behalf who'd been in heavy contact with his father. Worse yet, Akasaka decided to have Aqua have a change of heart, desperately try to save himself from dying only to fail and drown painfully in the water full of regrets.
Akane who's sole purpose in life after Aqua dumps him is to "thwart Aqua with her plan that'll stop him from ending everything." just completely fails. She doesn't save him. She doesn't even get to try, and now gets to live the rest of her life knowing she failed someone she cared deeply for and it cost him his life.
Miyoko loses her son, who she has raised since he was five. She had heard from her estranged husband that Aqua was teetering on the edge but then then Aka forgot she existed and didn't use her at all, so she never follows up on that information and it leads to her son's death.
Kana not only loses the boy she loves, but she never even gets to tell him that she loves him, and not for a lack of trying either. She sent Aqua a message asking him out, and Aqua never replied. One of the things he says he'd like to do prior to his suicide is get back to her on that, but because Aka wanted a "shocking ending", Aqua effectively leaves her message unread and denies her all closure.
Ruby has it the worst of the bunch. Her mother was murdered effectively by her father, and now her brother has also been effectively murdered by him. There was only one person in the world she cared about really and that was Aqua. He also doesn't tell her anything before the suicide. Doesn't go to see her last show. Like Kana, Ruby gets literally zero closure. Her one mission as a character was to become the Idol her mother never could, one that doesn't have to tell lies. It is explicitly shown that Ruby
never recovers and lives a life lying about her happiness to her fans. She is exactly what Ai was.
Oshi No Ko's ending is not simply bad. MH:A's ending was bad. JJK's ending was bad. Oshi No Ko's ending is actually gross bordering on offensive. It kills a main character with very little reason in an extremely agonizingly painful way and it does so in order to upset the reader. Akasaka skips so many steps and so much character development to get there. The suicide isn't earned or even necessary and it feels like it was done specifically to bother people. It very arguably glorifies suicide for the first half of the like three chapters Aqua's dying in only to, at the eleventh hour of the story rug pull and make Aqua regret it, again likely just to stick the blade into the audience again.
Every single character without fail ends up worse off. Director Gotanda, Aqua's surrogate father? Feels like he lost a son. Aqua's Half Brother? Loses the only family he really knows he has. Ruby's friends at school who are collectively in like four chapters? They get special mention about how it still bothers them sometimes.
To put a TL

R on all of this, Stephen King once said of the Shining Movie that it was "made to hurt people." I think Stephen King is a colossal faggot, but the ending of Oshi No Ko was absolutely designed to betray the audience and hurt them as much as possible for having given a single shit about this Manga. Aka Akasaka is a piece of shit and I will not be reading any of his future manga going forward.