HUMANITY

The Red Core is unlocked after completing Sequence 7. It is the final level and boss of the story. As you fight this boss, you will do damage to them and gain more followers in return. When you take damage, you'll lose followers. You need to defeat the boss by doing enough damage without losing all your followers.

Here is a full video walkthrough with all solutions, all Goldys, and achievements! (Timestamps in YouTube Description)

Story related, defeat the Red Core and it pops.

Here's how I tackled this one, starts at 4:28:32

4:28:32 - RED IS DEAD ACHIEVEMENT