This Mermaid Is Just That Mighty and Magnificent

A tough, straight-laced guy accidentally transmigrates into a danmei novel about a merman adored by all, becoming the merman bottom with a script that makes everyone fall for him. Every man he meets, without exception, wants him to lay eggs for them. The protagonist can't take it anymore. He shows off biceps bigger than any of theirs, an eight-pack, and his indescribable muscles. “Are you sure?”