>>536296568
When it comes to charisma, I think she's partly just a quieter, fairly blunt person on her own so you're probably not going to get her being as verbally engaging as others. Mikoto wants to inspire people with her performances, but she isn't really going to wow people with her MC prowess like Nichika.
Part of Mikoto figuring out her own self comes from actually getting a life and engaging with other people so the best way to boost her charisma is ironically exposing her to other people's charisma. Despite this, I still find it amusing how things sometimes go way over her head when you expose her to exactly that.