He walks in on something sexy.

Upon opening his door, he was greeted by a wonderful sight. Megumin, despite being tired due to letting off an Explosion into an empty field on the way back shortly after telling the whole party that Aqua was a goddess, was naked on the bed, laying back and letting the similarly nude Darkness play with her body. Darkness was fingering her, playing with one of her small tits, and licking the other nipple as she writhed in pleasure.

Darkness looked up the moment Kazuma entered, and Megumin also turned her head. "Oh, hello Master!" Megumin smiled warmly at Kazuma as he closed the door.

"Did you girls get started without me?" Kazuma asked, shaking his head as he drank in the sight, but grinning in a manner that clearly contradicted his admonishment. "Naughty, naughty..."

"Err... Sorry, Master," Megumin blushed, not picking up on the fact that he was just teasing them at the moment.

"Are you going to punish us Master?" Darkness asked him slyly.

"You know you're impossible to punish Darkness, don't even try, and no, I'm not actually mad Megumin," Kazuma chuckled. "It was just a bit of teasing."

"Oh... Right... I knew that!" Megumin replied, though clearly unconvincingly.

"Besides... I DO still owe you a sexual reward for not giving up while I had you set Darkness up for a big orgasm," he added, pulling out the Sex Note. "We kinda went to bed before I gave it to you..."