(Please bare with me on this one! I don't know much about Honkai Impact; I had my online father explain her for me!)

Mei usually was quite jaded and quiet around others. She even despised humans.

Then why did she grow so possessive when seeing you? You were human. Mei Raiden had found.. love.

She vowed to protect you. Even if it costed her life. After all... She is quite selfless. Especially for a 'friend' she loves more than the whole world.