Z Fighters

Krillin has a different form of friendship among the Z Fighters, if you think there is some form of friendship between all of them. Piccolo and Krillin I think have a stronger friendship than out of any of the Z Fighters (or former members) than besides Goku and Gohan.

-Piccolo and Krillin "befriended" each other during the fight against Nappa and Piccolo on more than once has saved Krillin's life. I would say they both gained great respect for each other over the serious battles they had together. Later on actually, Piccolo saved Krillin several times either in episodes or movies, so Piccolo watches out for Krillin. In return, Krillin looks to him for some experience at times. They both are very protective over Gohan and even though Krillin tried to save Gohan in the World Tournament Saga, Piccolo held Krillin back (more so to keep him from interfering, but Krillin could have been injured trying to save Gohan as well).

-Yamcha and Krillin have a simple friendship, as most people who would as they both trained with Roshi together for three years and you could describe it as a "school mate" friendship, maybe a bit stronger. Krillin lashed out from Yamcha's death in the early part of Z, but there are only a few other times you see their friendship strong like that.

-With the Crane Students, I would say that Chaozu and Krillin's small friendship faded over time that it appeared in Dragonball. Krillin, with what little screen time he has with Chaozu, there isn't much talk nor a strong hint that the friendship is as strong as it was when they were younger. Tien and Krillin, however, I do not really see any form of friendship, even though it is still there. Each of them respect each other. I think their friendship is simple and friendly, but not much there for fans to see. Tien does ask Krillin after he tries battling Cell if he was alright, which Krillin thanked him for.

-Vegeta and Krillin's 'relationship' is hard to describe. Vegeta sees Krillin as a coward while Krillin sees Vegeta as an annoying Saiyan (at least, early Z). I do believe their interactions are brought on simply by Vegeta scaring Krillin and Krillin hoping not to get killed by the Saiyan Prince. I have no doubts though, a somewhat stronger friendship formed by the time of the Majin Buu arc, because when Goku tells that Bulma, Krillin, Chi-Chi, and the others were done in by Majin Buu, Krillin is one of the people that he seems shocked to learn about after Bulma.

-Mirai Trunks (Future Trunks) and Krillin have a small friendship that is formed very quickly. Mirai Trunks and Krillin have the same overview on most of the events during the Cell/Android arc, so I have no doubt they formed a minor friendship during that time.