I Became the Secretary of a Hero!

I Became the Secretary of a Hero! (勇者様の秘書になりました, Yūsha-sama no Hisho ni Narimashita) is a light novel series by Tsukasa Yamazaki, with illustrations by Kiyu Kanae. Cross Infinite World is publishing the volumes digitally in English.

Plot
Paralegal Aki Konishi returns to her apartment after work to find a tall, dark, and handsome man claiming her little sister is his bride...before leaping out the window with her in his arms! Aki pursues the kidnapper through a rift he opened in the fabric of reality in a desperate attempt to save her sister.

Along the way, Aki encounters a dashing hero, a manly mage, and a handsome priest who unwittingly drags her into their battle against the Dark Lord, but what can a normal office worker do to help a hero and his team? Become the hero’s secretary, of course! Will Aki ever be able to save her sister from the Dark Lord?

Official
Official English site