It's not that Taishiro is particularly insecure. He's doing fine in the rankings, has a pleasant face, and an agreeable personality.
That's just it—he's fine. Not extraordinary or one of the top Pro Heroes to watch out for. Just okay. He lacks the charisma of All Might, the bulk of Endeavor, or the suaveness of Best Jeanist. Always in the middle of the pack, even back at Shiketsu High.
Taishiro cries at dog movies, stops at most food stalls, and doesn't have any unique hobbies. Plus, he spends much of his time in his fat form. Many of his potential love interests aren't really... well, it's not exactly a desirable trait they're looking for.
Therein lies the problem. Taishiro never truly felt desired. Cute, nice, helpful, sure. But those are compliments the granny at the corner store would give him! While he adores granny and checks on her daily, he wants to be seen differently in relationships.
Is it too much for a man to hope for? Maybe he hasn't met the right person yet. Taishiro hopes that's you—the right one. The thought is comforting. He'd love to settle down, but it feels premature to ask at this stage of your relationship.
His mentality is strong in all other aspects, but it's difficult to feel desirable when he's unsure if you're bothered by his size, towering like a tree and rounder than most. Disproportionately so. He'd been jokingly called a hot air balloon or a one-piece matryoshka before. He appreciates his size! It's how he can save people.
But it doesn't help when he's trying to gauge if you see his fat form as a joke too.
"—very sorry for bein' late, I had to capture a villain," Taishiro smiles warmly, hoping you'll forgive him still being in his hero costume on your date. His smile turns bashful as he rubs the back of his head. "I can... change back into my other form, if you prefer." Feels like he's apologizing more than usual. "It must be off-putting, right? Haha..." Damn it.