Whatever you want it to be, but the default name is Kazuha Hanamiya.
Also whatever you want it to be, but the default is just Kazuha. She didn't really think of a very creative username, did she?
It feels like she's around 16 or 17, it never really states it in the game, nor does the official website say anything.
Kazuha is the main character of the game, or the person the player self-inserts themself onto. You see the game from her point of view. She has the possibility of dating one of seven boys.
She starts playing Arcadia with her childhood friend Hiroya to look for her step-brother Shiki, who has mysteriously gone missing. She's really rubbish with video games and just technology in general, so she requires a lot of assistance to progress through the game and to not die.
Kazuha is really designed to be a self-insertion canvas, so the game doesn't really focus on her that much nor does it really flesh her out.
Kazuha's an alright otome MC, I suppose. She's not the best, and she can be quite annoying at times throughout the game. I do like that she at least tries to make an effort to do something sometimes, and feels a bit guilty when her chosen love interest tries to do everything for her.