The Mare Ball (メアボール Mea Bōru) is a ball-shaped superweapon appearing in Keroro Gunso the Super Movie 2: The Deep Sea Princess de arimasu!. It is the counterpart of Keron's Kero ball. It is mentioned that it is capable of drowning a whole planet with water, thus granting Maronians domination over it.
It looks exactly like Kero ball, except its red-colored with many blunt triangular buttons surrounding it with a picture of a Maron emblem and other logos on it. It has an antenna with a blue circular tip.
- A Mare ball will only shapeshift into a random sophisticated weapons when anyone holds it in his/her hand and it glows.
- When Meru is making any wish from Natsumi's memories, it glows yellow and the wish will come true and turns real, but it soon wore off after Meru and Maru goes back to Maron.
- The Mare ball acts like flashlight underwater.
- It also has an ability to transform Meru into more human then later into a giant mutated monster, but soon gone berserk due to reacting to Meru's emotions, and starting to control him and making him grow more until it forms a giant portal leads to an endless abyss, but he soon return to his original form after, while he's unconscious along with Maru, who is also unconscious as well.