Collect all Vestiges before each boss fight and restore all Successors in the memory scenes during a single playthrough to unlock the "Dwellers" ending, which is the true (best) ending in Code Vein. To save the Successors, thoroughly search the areas before their boss fights. There are special memories called Vestiges. You need to find all of the boss's Vestiges before defeating them in battle. Collect all the Vestiges, then give them to the NPC that resembles Io to save the Successor, freeing them from stone. Since you must save every Successor in the game, you need to carefully explore every area before defeating the boss.