A Simple Task of Providing Support From the Shadows to Defeat the Demon Lord

This fantasy series begins with a holy warrior summoned from an alternate world to defeat a demon lord. Ares, a priest ordered to support the holy warrior, is shocked at the sight of his party members: a mage who can only use fire spells, a sword fighter who just transfered schools, and the holy warrior himself who repeatedly the same rash actions over and over. Unconvinced that they will succeed, Ares conceals his skill levels and follows behind.

(Source: Yen Press)