Lancer

Lancer is an enemy Servant in the Moon Cell Holy Grail War in Fate/Extra CCC. She is unique in that she switches between four different Masters as a Lancer-class Servant, Rin Tohsaka, Rani VIII, Shinji Matou, and Hakuno Kishinami, and she later acts as the Berserker-class Servant of Meltlilith. She is one of the Servants of the Protagonist of the Grand Order conflicts of Fate/Grand Order under both the Lancer class and Caster class.

(Source: Type-Moon Wikia)