The Attack Titan of Darkness: Saving Mikasa from the Start

Lin Yu and Eren go through another cycle of reincarnation, and Eren gradually grows numb and indifferent within it.

He begins controlling his own father, turning him into a Titan to carry out certain plans, all for the sake of achieving the goal in his heart.

His family and friends gradually become dispensable as the cycles go on. In the end, he follows the same old path and becomes...

Eren also forbids Lin Yu from helping his past self, but Lin Yu ignores him. When Eren sends the power of the Founding Titan to his past self, Lin Yu sends power to his own past self as well.

Lin Yu knows that the point of enduring painful cycles is to change things, not to let the cycle continue forever.

So when Eren sends the power of the Founding Titan to his past self and awakens, Lin Yu transfers the powers of all Nine Titans to his own past self, giving him the chance to change the tragedy.