Gamatatsu

is one of Gamabunta's children and Gamakichi's younger brother who has a fixation with snacks.

Personality
Gamatatsu is potrayed as being even more 'simple' and 'stupid' than Naruto is. In his first appearence, Gamatatsu shows that he'd choose snacks over someone's life; when Naruto was injured while fighting with Kabuto Yakushi, he asks; "Hey Gamakichi, do we have to wait for the kid to croak till we get snacks, cuz' I'm getting hungry". Although in the filler arcs, Gamatatsu showed that he does care about Naruto's life as he was ready to rescue him before Gamakichi talked him out of it. While being naive and childishly stupid, he does sometimes make use of his natural curiosity to help Naruto solve puzzles (like the mystery of the Ghost Warrior in the Land of Birds arc).

Gamatatsu's obsession for snacks is so great that he waited a year since his first summon for the snack he was promised, even though he didn't get it. He is always hungry and asking his summoner for snacks, and often gets mixed up in unusual predicaments in which he counts on his "big brother Gamakichi" to get him out of. In the English anime, his voice is jocularly high. He also openly refers to Gamabunta as "daddy", which the older toad either chooses to ignore or simply doesn't mind.

Gamatatsu seems to lack a sense of danger. When Orochimaru summoned Manda, Gamatatsu was too busy saying hello to his father to notice that the giant snake was staring at him. The young toad did not seem frightened in the least until Gamakichi told him to run. However, this fearlessness may also have been due to his titanic and overprotective father's presence or his lack of sense of endangerment.

Part I
Gamatatsu was accidentally summoned by Naruto Uzumaki during a battle with Orochimaru in an attempt to compensate for Jiraiya's failed summoning. He was summoned again with Gamakichi by Naruto during the Land of the Sea arc for a scouting mission. Gamatatsu makes a short appearance in the Land of Birds arc when Gamakichi and Naruto need him. Despite Naruto thinking he will be helpless Gamatatsu, using his curiosity, finds a kite as a clue about how can the Cursed Warrior fly. Later, he goes down a dark tunnel with Naruto and Gamakichi and gets caught by the Daimyo and the guards. These event have led Naruto to believe that Gamatatsu can be helpful.

Three-Tails Arrival filler arc
Although he does not have his Part II debut until much later in the manga, Gamatatsu appears sooner in the anime adaptation. When Naruto proves incapable of synchronizing with Gamariki for combination jutsu, Naruto decided to summon Gamakichi and Gamatatsu as he has worked well with them before. Naruto was amazed at how much they both grew as they were bigger than him now, which Gamatatsu remarks to be because of all the snacks they've eaten. Naruto then learns that neither Gamatatsu or Gamakichi have mastered water-based abilities like their father, but decides to continue working with them, since Naruto finds it more preferable than working with Gamariki.

Deciding to try and learn water element, Gamatatsu begins getting trained by Gamakichi with what appears to be the basics of water-chakra learned from their father. After several failed attempts at water-chakra which involved using already existing water stored in Gamatatsu's mouth, he finally manages a powerful water blast. Later, when Team Yamato find it impossible to break through Guren's crystal barrier via conventional means, Naruto summons Gamakichi and Gamatatsu to help. Gamatatsu uses his newly learned water blast to break through Guren's crystal, and subsequently helps rescue Hinata. After their job is finished they return home.

Unfortunately, Naruto repeatedly calls him and his brother back again to aid him during the mission. Naruto calls the two brothers to aid him in crossing a lake and defending the seal for the Three-Tails.

Quotes

 * "How you doing, Daddy?"
 * "Can I have a snack?"
 * "This is the first time anyone's ever summoned me! I'm finally getting a chance to shine!"