In the early series Yamcha and Krillin would be this for Goku, after getting over their initial dislike and becoming Fire-Forged Friends. Usually giving him advice on normal human life, most importantly telling Goku to put clothes on when naked in public.
Bulma can be seen as Cool Big Sis to Goku despite being closer to her in age, Bulma washing him in the bath is quite sweet in retrospect.
Tien towards Chiaotzu. Despite respecting their sensei Master Shen the Crane Hermit, Tien becomes furious when his master attacked Chiaotzu and when Tao defeated Chiaotzu in the Tournament after that, Tien avenged Chiaotzu with righteous fury.
Despite being monsters Tambourine cared deeply when Cymbal was killed by Yajirobe.
While Goku and Piccolo are Papa Wolf to Gohan, Krillin is definitely a kind of uncle/big brother to Gohan, especially on Namek and Dende as well for that matter.
For all its dumb moments, the Garlic Junior Saga really pushes Krillin’s protectiveness of Gohan to the front lines. He tries to shield him from Chi-Chi’s anger, guides him as they go to fight Garlic Junior and even throws himself in front of him to protect him. Gohan returns this by being very outwardly affectionate to Krillin, even jumping into his arms at the end of the battle.
This saga also provides an inverse of this trope, where one of the main reasons that Gohan won’t attack at the end is because he refuses to lower his shield that is protecting Krillin and Piccolo. They eventually have to jump out of its protection to force Gohan’s hand.
Future Gohan to Future Trunks (mostly in the History of Trunks special), not only mentoring him, but Gohan used the last senzu bean he had to heal Trunks after getting blasted by the Androids despite Gohan being the one with the missing arm. Future Gohan truly believed Trunks would save their timeline and when Trunks tired to go with on his last fight with 17 and 18 he knocked him out for his own safety.
Present Gohan becomes this, most notably shown in Dragon Ball Z: Broly – Second Coming where Gohan flies in to fight the titular villain when he attacks Goten and Trunks. Bulma even tells Tapion in Dragon Ball Z: Wrath of the Dragon that Trunks is actually jealous of Goten for having such a cool older brother. Tapion fills this role for Trunks, especially since he couldn't protect his own little brother Minotia.
