On the planet of festivities where people live in a dream, we finally unravel the mysteries of the mastermind behind it all. The main story sets the grand stage where you confront Sunday, who becomes a repeatable boss in Honkai: Star Rail.

The Great Septimus of the “Harmonious Choir” is one of the toughest bosses in Honkai, so you’ll need all the help you can get to defeat him. Here’s where to find the Great Septimus, how to unlock him, how to defeat him, and more.

You unlock The Great Septimus boss by playing through the main story of Penacony. After completing the mission "And on the Eighth Day", you will face Sunday, who transforms into the embodiment of Harmony and Order. After defeating him, The Great Septimus becomes a repeatable boss where you will receive valuable materials for new characters.

The boss is located in the new zone of Honkai's 2.2 version, Penacony Grand Theater. As the name suggests, it is a giant theater where you fight the boss on the main stage. To reach the boss, go through the hallway, down the stairs and then straight to the stage. Once you unlock the boss, you can teleport directly to it at any time.