Banished from the Hero's Party, I Decided to Live a Quiet Life in the Countryside, Vol. 5 (manga)

Though Red and Rit have been enjoying their new, stress-free life together in Zoltan, the Hero, Ruti, hasn't taken her brother's departure nearly so well. Nevertheless, she and her party head for an ancient ruin in search of a weapon left behind by the demon lord-though what they find may not be quite what they expected...