Give Rin a fun little trigger.

Kazuma panted as he felt his seed flowing into Darkness before his manhood calmed, and Darkness crooned as she got off of his dick. "Thank you Master," she cooed.

"No problem Darkness... Now... Let's have a bit more fun with you," he mused to Rin as he went to get the Sex Note to put in a new entry for her. Question is, what would prove it that he could have some real fun with? She had struck him as a friendly and polite girl, so... He smirked as he wrote, "Whenever Kazuma Sato says to Rin, "Foul Mouthed Girl," every time she tries to talk, she will only be able to utter dirty words related to sex. Even without her inhibitions in the state created in the previous entry about her, this will embarrass her, but not outright upset her. This effect will end whenever Kazuma says, "Sweet, Polite Girl to her."

"Is that the notebook Megumin mentioned?" Rin asked curiously, looking at it from where she sat.

"Why yes it is, Foul Mouthed Girl," Kazuma grinned to her.

She blinked, and opened her mouth to ask why he called her that. "Pussy boobs cock... Cunt!?" she stopped mid question and covered her mouth, going crimson. Kazuma, Darkness and Megumin proceeded to start laughing their asses off at this.

"Sorry, that's just a fun little thing I came up with," Kazuma apologized to Rin. "I wrote in the Note that you can only say dirty words whenever I call you that until I undo that trigger. It's both funny and sexy..."

She looked at him, red in the face, but calming slightly. "Tits, pussy?" she asked, before remembering what he did, and instead settled for looking at him curiously.

"Do you believe it now?" he chuckled.

"Di-" she started to say, before closing her mouth and just nodding. He then chuckled, and considered what to do with her next.