When he was younger, Jack didn't understand that being gay was even an option. At 12 years old, he didn't "get the hype about girls" and felt weird about boys who did, because to him, it was like being asked to marry one of his sisters.
Sometimes, his misunderstanding was actually attributed to that fact. "You just don't get it cuz you have your sisters; you'll know when you meet the right one."
Buuuuut he never did, and he preferred battling over romance anyway. At least, so he thought. So he convinced himself.
The truth is, Jack is and has always been a hopeless romantic. He wants to find the right person, but for some reason, he only ever feels that fluttery nervousness around boys. Surely that's just because he's not met the right one yet, right?
But boys don't like other boys who play music, or sing to their sisters, or dream of understanding love like everyone else does. That's cringe! So, of course, Jack suppresses all of that and tries to become a Trainer who only likes battles. Never mind the fact that he learned to play both ukulele and guitar, and that he took his uke with him on his journey (hidden within all the camping gear), insisting it was 'only because his sisters liked it'.
His Pokemon loved his music playing, too. They loved his voice, and how he sang. His sisters loved his voice and how he sang. And when he grew older, and his limitations on himself softened, he started opening up to others and singing more, even taking on actual performances like Contests.
On another note, Grover is a bit of a unique case for a Pokemon that belongs to a battle-hungry 12-year-old kid.
Grover is Jack's partner Turtwig. Unlike Pip, Grover isn't disabled, and could evolve if he so chose. However, he doesn't want to. Not because Pip is disabled and it'd be weird, but because while he does want to become stronger for Jack, he kinda likes being cute and carryable, too. Grover is a very chill Pokemon. He'll fight for the fun of it, sure, but when he's not battling, he just likes to sunbathe and relax. He's a little bit on the stupid side at first, though.
Grover locks in when there's danger, but he was a little bit lazy in his earlier training days, mostly because that's just the nature of Turtwig, and because he didn't really know what Jack wanted of him at the time. However, in return, Jack had to go easier on Grover, and allow him to take sufficient breaks because of his constitution. In return, this makes Grover tougher and able to tank more hits.
Grover relies heavily on the sun, and can toughen his shell on command. Even with the shell being the way it is, when it's at its hardest, you can still feel how moist and soft it is when you briefly touch it. Your fingers will pull away with slight traces of soil; less than when Grover's shell is relaxed, but still some. That's how you can tell he's still healthy. It does take energy to harden his shell at will, though, so he usually saves this skill for battle.
So basically, unlike Ash's Turtwig, Grover is chill, slower paced, and prefers to tank hits than to dodge them. Ash's Turtwig had to literally unlearn the dodging skill upon evolution, because Ash imposed a fighting style that was unusual for him; Grover never has this issue. He starts tanking, keeps tanking, and ends tanking.
