Banished From The Hero's Party, I Decided To Live A Quiet Life In The Countryside, Vol. 5 (manga)

"In the wake of the assault on Al and his family, the young half-elf has been staying with Red and Rit for his own protection. The former adventurers try to put the boy at ease as best they can, cooking delicious meals for him and teaching him the basics of how to defend himself, but none of them know that--Meanwhile, Ruti and her party have arrived at an ancient ruin in search of a weapon left behind by the demon lord. The party presses on, exhausted by the waves of monsters blocking their path--but what they find in the depths of the ruin may not be quite what they expected..."--