This Krillin comes from Universe 13. His history is very different compared to his other counterparts, as Gokū did not become a student of Roshi.
This Krillin seems more caring and polite than his Universe 18 counterpart as a child, as he deeply cares for Kakarotto's safety. He also seems to be very playful with Kakarotto, due to Krillin spitting water in his face while in the river.
Universe 13 Origins - The Friend
In Year 751, Kakarotto transforms into a Great Ape, and begins destroying many villages. Master Roshi and Krillin begin to investigate. Roshi tells him to go to search for survivors. He warns Krillin that this is no mere beast, that it is a trained killer. Krillin finds Kakarotto, having flashbacks from his mother, telling him to kill. He then sees Krillin, Krillin asks Kakarotto if he is okay. He tells Kakarotto that they should go see Master Roshi. Kakarotto senses that he is Human, and that he must kill him, but before he did so, he asked Krillin if he was a turtle, Krillin states that he is a proud member of the Turtle School, and Kakarotto walks off. Krillin thinks to himself that he must be one the surviving villagers that got attacked by the beast, not knowing it was actually Kakarotto that was the beast. Krillin tells him that they must stay together, he says that there's a river nearby, and he should wash up. Misinterpreting the answer and believing Krillin to be a turtle, Kakarotto thinks to himself, that turtles indeed love water. Kakarotto and Krillin then see Roshi, Krillin tells Roshi that he has found a survivor. Kakarotto then states that Roshi looks a lot like a human. Roshi then says he is human, then Kakarotto, enraged, attacks Roshi. As they begin to fight, Roshi states that Kakarotto's power is enormous for his age. He then realizes that Kakarotto, is the beast that attacked the villages. Krillin then grabs Kakarotto, begging him to stop, however, Kakarotto pushes Krillin off of him. As they fight, Roshi defeats Kakarotto. Realizing that he is the beast, he says that he will attempt to help the poor boy, and give him peace. As Kakarotto regains consciousness, he runs into a cave, Roshi states that it is a trap. Kakarotto and Roshi fight, and Kakarotto, after a short battle, is the victor. Kakarotto then says to Krillin, that he must kill all humans, and one day, he will kill him as well. Krillin then vows he will kill Kakarotto one day.