Prior to the events of Octopath Traveler, Gustav joined Werner’s band of mercenaries, the Black Brotherhood. He and Gaston made friends with Erhardt, who acted as their mentor as they were new to the group. The group disbanded after the fall of Hornburg, and the mercenaries went their separate ways.
Gustav ended up in Victors Hollow, where he makes a name for himself as a fearsome new competitor in the arena. He faces off with Olberic in the finals, and upon losing to him, agrees to disclose Erhardt’s location and reason for vengeance.
After Olberic's story, he appears in The Whistlewood, vowing to repair his reputation.
Gustav will begin battle by increasing his actions per turn to 2. All of his weaknesses will be locked. Upon defeating one of the two Shield Warriors, he emotes Gustav Let His Guard Down!, which will unlock Gustav's weakness to axes and dark damage. When both Shield Warriors are defeated, he emotes Gustav is Defenseless!, and all of his weaknesses will be unlocked.
- Level Slash: Physical attack, targets entire party.
- Cross Strike: Heavy physical attack, single target.
- Triple Strike: Physical attack, single target. Three consecutive hits.
- Black Blade: Physical attack, single target. May inflict terror.
- My Blade Sunders All!: Used at 50% health, increases actions per turn to 3.
7910 HP. Shield 5
- Charge: Physical attack, single target.
- Shield Bash: Physical attack, single target. Augments user's defense for 2 turns..
- Extreme Charge: Heavy physical attack, single target. May inflict unconsciousness.
- "I may be bested, but I be not defeated. The Black Knight will not see the name tarnished again." —Speaking to Gustav (The Whistlewood)
- "Take what you need." —Purchase
- "My arm is yours, should you have need of it." —Guide/Allure
- "Off I go." —Part Ways
- "I’ll give you a good fight!" —Challenge
- "Do you yield?" —Provoke
- "Such antics are the mark of a dullard!" —Failure