Bofuri: I Don't Want to Get Hurt, so I'll Max Out My Defense., Vol. 12 (light novel‪)‬

Sunken ships, lost treasure, and underwater adventure!Maple Tree arrives on the eighth stratum to find a whole new world under the sea. They’ll have to dive deep to explore and master fighting in the water. Maple’s defense build isn’t designed for the speed and agility required to swim, but she’ll find a way! Thankfully, Sally’s already a skilled swimmer. With her help, the rest of the guild heads out to find what awaits them on the ocean floor—and what lurks in the dark depths...