Banished from the Hero's Party, I Decided to Live a Quiet Life in the Countryside, Vol. 4 (manga)

"In that case, let's just forget about work and relax!" And just like that, Red and Rit decide to play hooky from their shop to go on a riverside date, where— "hey, let's swim!" Quality time with a princess in a swimsuit proves to be a much-needed balm to our protagonist's heart. But not all is fun and games, as the rapid proliferation of a dangerous drug among the populace of sleepy Zoltan leads to a rash of disturbing, violent incidents...

Volume 4 of the Banished from the Hero's Party, I Decided to Live a Quiet Life in the Countryside manga series by Masahiro Ikeno.