Honkai: Star Rail: The Great Septimus boss guide and how to beat it

On the planet of festivities where people live inside of a dream, we finally unravel the mysteries of the mastermind behind it all. The main story sets up 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 hardest bosses in Honkai, so you will need all the help you can get to take him down. Here’s The Great Septimus’ location, how to unlock it, how to beat it, and more.

How to unlock The Great Septimus boss in Honkai: Star Rail

You unlock The Great Septimus boss by playing through Penacony’s main story. Upon finishing the “And on the Eighth Day” quest, you face Sunday, who transforms into the embodiment of Harmony and Order. After you beat him, The Great Septimus becomes a repeatable boss where you get valuable materials for new characters.

The Great Septimus boss location in Honkai: Star Rail

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

The Great Septimus boss mechanics and how to beat it in Honkai: Star Rail

The Great Septimus has three phases, each with a different Imaginary attack. He deals single-target and AoE damage, stuns party members, ignores their defense, and can shield himself. While this boss is tough to beat, he also has weaknesses you can exploit. All party members gain a shield after destroying all four of his summons, increasing the Break Effect of The Great Septimus.

Phase one

The starting phase is straightforward because the boss only uses three attacks that follow the same pattern. He first uses a single attack and then an AoE attack, In the next turn, he stuns one of your party members, greatly increasing damage taken by them for at least one turn. The boss also summons four “Echoes of Faded Dreams,” which you can destroy to gain shields and an extra turn. Additionally, whenever The Great Septimus gets weakness broken, all party members gain a shield that absorbs all incoming damage. 

Phase two

Phase two is the hardest one of the entire fight. Not only does the boss use the same attacks from phase one, but he also shields himself, absorbing all the damage you throw at him. The easiest way to destroy his shield is to break his four summons and attack him. Once the shield goes down, his weakness break gets greatly increased, so make sure to dish out a ton of damage to burst him down.

Phase three

Surprisingly, phase three is the easiest one. After changing his name to “Embryo of Philosophy” Sunday, the boss only does one type of attack. He automatically enters a charge state for seven turns, after which he does a massive Imaginary AoE attack. While a good shielder can protect you from his strongest attack, it’s better to prevent him from using it by breaking his charge state. 

Best characters to use for The Great Septimus boss in Honkai: Star Rail

While The Great Septimus deals Imaginary damage, that’s also his biggest weakness. During the first two phases, the boss is vulnerable to Fire, Lightning, and Imaginary elements. Additionally, in the third phase, his weakness is increased to all Elements, allowing you to be flexible with your characters. If you want to take him down, you need a strong DPS and preferably a good shielder. Here are some of the characters you can use:

• Fu Xuan
• Acheron
• Kafka
• Aventurine
• Dan Heng Imbibitor Lunae
• Welt
• Himeko
• Topaz and Numby

What does The Great Septimus drop in Honkai: Star Rail?

Because The Great Septimus is a weekly boss, you can only fight him three times per week, and to claim rewards, you need to spend 30 original Trailblaze Power. You can obtain the following rewards: 

• Lost Echo of the Shared Wish
• The Ashblazing Grand Duke relic set pieces
• Watchmaker, Master of Dream Machinations relic set pieces
• Lucent Afterglow
• Abundance Light Cone called “What is real?”
• Harmony Light Cone called “Dreamville Adventure”
• Hunt Light Cone called “Final Victor”
• Destruction Light Cone called “Flames Afar”
• Preservation Light Cone called “Destiny’s Threads Forewoven”
• Erudition Light Cone called “The Day The Cosmos Fell”
• Nihility Light Cone called “It’s Showtime”
• Credit

Only Robin uses the new ascension materials, but considering how The Great Septimus is the only weekly boss of Penacony, it’s safe to say that future characters will use them as well, so you’ll have to fight this boss frequently.