Oneesama to Watashi: Ojousama ga Isekai Tensei

Reincarnated in another world, Hinako declines the cheat-like powers offered to her and instead takes a vow of sisterhood with the giant Ellis, becoming known as the Smallest Giant. A prim and proper lady might not have a lot in common with a fearsome titan, but the two share a goal: searching for those who once meant so much to them. However, they must be cautious, for just as their strength wins them fame, it also captures the attention of an ill-mannered paladin...

(Source: Yen Press)