Black Marlin was created using a body part of a dangerous aquatic beast that had the ability to control water. Some time before the start of the series, Liver got a hold of the Teigu and used it in many battles alongside his comrades. After his death, the Teigu was repossessed by the Revolutionary Army. During the rebellion against The Empire, one of higher ups notes to Honest that Black Marlin, along with Scream and Extase, is being used by revolutionaries against the Imperial army.
The user can control any liquid around, including water and blood by simple hand gestures. However, it only functions in the presence of water or any other form of liquid around. Oftentimes, the water takes the shape of serpents or dragons.
- Water Barrage (水砲弾, Suihōdan): The user manipulates huge amounts of water around him to gather and shoot it in multiple streams at the target.
- Serpent of the Abyss (深淵の蛇, Shinen no Hebi): The user manipulates the water to form a giant snake out pressured water and fires it at the enemy.
- Murky Lance (悪龍槍, Aku Ryūsō): The user quickly launches multiple streams of water at a target.
- Water Dragons Divine Conquest (水龍・天性, Suiryū Tensei) The user launches ten streams of water at the target in the shape of dragons. This attack seems to be very powerful. This attack is strong enough to destroy Incursio.
- Blade of Blood (血刀残, Kettōsan): The trump card of Black Marlin which allows user to manipulate their own blood. After user bled through injury, they harden and shape their own blood in the form of blades to cut the opponent. The blades are strong enough to clash with a Teigu.