first he gives Max a much-needed What the Hell, Hero? about the way he's trying to gain time for Rei and Takao (who are late due a chili pepper and an avalanche), as he's disrespecting his opponent in the semi-finals, an opponent who had to assemble a beyblade by scavenging parts from a beach (there were no beyblades in the Maldives).
when Max finally wins, Takao and Rei still aren't there... So Kai, who so far had not fought due a lack of capable opponents, finally competes. And saves Max from an embarrassing situation in the process;
finally, refusing to disrespect his opponent by going easy on him, wins with his usual One-Hit KO... But, differently from usual, opts for a ring-out instead of the usual disintegration.
Also, after the match, Max gives his opponent his old beyblade, the Draciel Metal Ball Defenser. Sure, he has Draciel S now... But he did put the Metal Ball Defenser together on his own.
The entire episode 16 of season one, as it deals with Rei and Mao's relationship. It's beyond this troper's ability to describe, except for the climax: their reciprocal Anguished Declaration of Love.
Also, Kai encouraging Rei to snap out of his funk and fight for his dreams. And when Rei does that, Kai smiles. Not his usual superior smirk, just a calm smile.
He continues giving advice and encouragement in episode 17 too, but this time is to Takao, his rival.
In episode 18, Takao, Max and the Chief stopping whatever they were doing just to help a little kid to repair his beyblade. The fact they ended up creating 10Bistool (one of the best beyblades of the plastic era, in the metagame) makes this only more heartwarming.
The reunion between Max and his mother in episode 19. Quickly turned in a Tear Jerker when she learns Max is there with the Bladebreakers and goes into cold scientist mode.
Episode 21 offers us Kai playing Trickster Mentor to Takao and helping a beginner at the same time.
Max's mother finally showing some concern for her son after their first encounter.
Kai taking care of telling Max where his mother is in the audience.