>>34322192There's a somewhat common trope in Japanese media called chuunibyou. It involves a character, typically a school-aged boy, acting overdramatic or edgy and pretending things are a lot more intense than they really are. Chuuni is closely associated with overdramatic hand movements, such as what Gladion employs.
If you've ever played Fire Emblem Awakening, Owain is a light-hearted example of the trope. Gladion is kind of unique in that he initially gives off a strong chuuni vibe but it turns out he actually has some reason behind his behavior rather than being a goofy attention-seeker. In the case of his hand movement I'd guess it's awful nerves or anxiety.
