Itsuki Mizuho 
To Another World… with Land Mines! Volume 7 [EPUB ebook] 

Nao and his friends return to Laffan for a short break before accepting a new quest to retrieve a sword—a prized family heirloom that belongs to the House of Nernas. The sword apparently went missing at the abandoned mine they briefly checked out once before, but upon further exploration, they discover that the mine is really a full-blown dungeon! On top of that, they meet Mary and Metea, two sisters who were chased from their home in Kelg because of the Holy Satomi Sect. Trouble just seems to follow Nao and his friends wherever they go, making their dream of an easy life feel further away than ever!