Muryoku Seijo to Munou Oujo: Maryoku Zero de Shoukan Sareta Seijo no Isekai Kyuukoku-ki

One day, listless part-timer Tamura Nana was summoned out of her room and into another world, after which her summoners declared her a saint and asked her to save their world. However, though she was hailed as a saint, it turned out that Nana possessed no magical power at all! To make matters worse, she was chosen as a partner by a princess who can't use magic... The helpless saint who has no magic and the powerless princess who can't use magic. And so begins the adventure of these two leftover heroes! (Source: Yuri-Hime, translated)