Post an anime character who shows some characteristics to prove that he/she is serious.

Yamamoto from Katekyo Hitman Reborn !

Normally Yamamoto is the constantly smiling one of the group who never takes anything seriously but when he actually does take things seriously then he can slice through multiple things with his katana and is skilled at using the rain flame . Also when serious Yamamoto becomes a little more ruthless and does anything in order to defeat the enemy .

Mirajane is one for me. Her carefree personality is sweet and kind. But is someone messes with her or Fairy Tail. She Transforms into her Satan Soul. A obvious sign of anger and seriousness.