I only played Code Vein this year and in fact i just beated right now.I knew about the endings and decided to go for the Dweller of Dark(good ending)for my first try even tho i'm a completionist when it comes to trophies. There may be a misconception regarding the secret ending and i will explain,but, you CAN restore a Eos vestige before the final fight and still get the secret ending in one go without defeating the boss a second time. The additional scene with Io counts as a fourth ending, meaning to get the Determiner of Fate trophy/achievement you'll need to do Dweller in the Dark twice, once seeing the extra scene and one without.By doing that, you'll have to find their respective vestiges and repair them before heading into the boss fight. You'll find an Eos vestige outside of the crypt for each Successor after their battle, while the remaining are found in Provisional Government Center. In order to achieve this ending, you'll need to save all four successors by restoring their memories after each battle against the successor. "Dweller in the Dark" is often viewed as the true ending of the game. If you repaired every Eos Vestige before the final boss, you will unlock an additional scene where before leaving, the Player stops, looks back, and says Io's name. The Player, Louis, Yakumo, Mia and Murasame then go through the hole and leave. The tree produces a single Amber Blood Bead that the Player uses to open a hole in the Red Mist, leading to the outside world. She then transforms into a massive Bloodspring tree that regularly produces Blood Beads, and maintains the Red Mist.
In this ending, the Player tries to take the Relics inside Silva's body, but is stopped by Io, which then begins absorbing all the Relics into her body, including the ones inside Aurora, Karen, Nicola, Emily, Eva, Jack, and the Player themself. DO NOT go through the large door at the end of each successors' memory. Restore all vestiges of the successors before their respective boss fights, then, restore the memories of each successor by interacting with their petrified body during their memory.It is also the only route where you don't fight the final boss' second form. To achieve this, walk past each successor and exit through the gate during each of their post-fight memories without restoring them. "Heirs" is considered to be the bad ending of the game. Io is last seen resting on the same Bloodspring the player saw at the beginning of the game, where the Player's weapon now rests. After this event, Louis takes Silva's place in the throne to maintain the Red Mist, while Mia, Yakumo and Jack replace Nicola, Emily and Eva as Successors. Louis is then forced to stab the Player through the heart to kill them. In this ending, the Player is unable to control all the Relics inside their body, and begins his/her transformation into the Queen. Walk through the door after the battle against a successor without speaking to their petrified body (which can only be spoken to if their vestiges were restored prior to defeating them).Do NOT save any of the four Successors.