Onee-sama to Watashi: Ojou-sama ga isekai Tensei

Reincarnated in another world, Hinako declines the abilities offered to her by the Goddess, and instead takes a vow of sisterhood with the giant Eiris, becoming known herself as “the smallest giant.” The two may be different species, born on different worlds, but they share one goal—searching for the precious siblings they lost. But they must be cautious, for just as their bond and strength win them fame, they also bring attention from the knights of the church…

(Source: Yen Press)