I'm thinking of making this AU and it's based around the Metal Bros. Shard, Metal Sonic, and Cyber all fell into they underground. Chara and Asriel find them both and take them to their parents, so they begin to get used to living here. Shard starts taking the traits of Asgore as Metal takes the traits of Toriel (Momma's Boy XD) and Cyber is most like Asriel.
One day Chara gets sick and soon dies but on purpose, to free the monsters. Cyber and Asriel share that power of Chara's soul and go through the barrier to find six human souls. The humans attack both Cyber and Asriel since they see them holding Chara's body, Cyber dies after being shot by arrows so Asriel takes both Cyber's body and Chara's back home.
When Asriel arrives he dies dropping the bodies of both, Metal, Toriel, Shard, and Asgore see all of them dead. Asgore goes into a rage and declares war against humans, Shard agrees but Metal doesn't. Metal and Toriel leave them to go live in the ruins, Toriel takes Chara's body and Metal takes Cyber's. Shard stays behind to live with Asgore and is later declared the new prince of the underground. While Metal is content with following Toriel.
Before Metal and Toriel left Alphys tested on a flower with determination while she made a robotic version of one and gave it determination also, she gave the mechanical one to Metal on leaves the other one in the garden. Metal plants the flower over where he buries Cyber, so the essence of Cyber goes into the flower reincarnating him. Same with Asriel.
In the beginning of the game you run into two flowers, the one that is robotic is Cyber, now called Pixel. And the other is Flowey. They both try to kill you but Metal and Toriel step in and save you.

There is also a version of this AU where Cyber becomes the narrator instead, like Chara. So there's no robot flower in it whatsoever. This would be cool if there were two players, one flower for each or one narrator for each.

What do you think of my idea? Comment and vote please!!