The Ink Tank is a cylindrical container made primarily of clear plastic, while its top and bottom are covered in green caps. Inklings typically wear an Ink Tank on their back during battle as a way to store ink. As Inklings use a weapon, the content of the Ink Tank visibly decreases. When an Ink Tank is nearly out of Ink, weapons can no longer be used in their regular state, and a notification appears, stating "low ink." Ink Tanks can be refilled slowly by ceasing to use a weapon, or quickly by being submerged in a puddle of similarly-colored ink. While submerged, an Ink Tank icon appears, displaying the current capacity of the Ink Tank. Using a Special Weapon immediately refills the Ink Tank.
The Ink Tank on the back of the player indicates the amount of ink in real-time. The Ink Tank will flash red when a player is out of ink. Upon using a weapon, the Ink Tank will temporarily stop recharging ink, showing a white space where the ink was used, until the player finishes. An LED on top of the Ink Tank lights up when there is enough ink to deploy the Sub Weapon. While recharging ink, a slight sound effect will occur when enough ink has been restored to use the Sub Weapon. A small red arrow on the Ink Tank indicates how much ink is necessary to use the Sub Weapon.
- Ink Saver (Main) decreases Main Weapons' Ink usage by up to 60%.
- Ink Saver (Sub) decreases Sub Weapons' usage by up to 75%.
- Ink Recovery Up increases the Ink Tank's refill rate while in squid form by up to 40%.
- Last-Ditch Effort decreases Ink usage for both Main and Sub Weapons as well as speeding up Ink recovery during the last 30 seconds of a battle.