It's set after the manga when Kenshin and kaoru first get married. Megumi show kaoru some 'educational drawings/paintings' on married life which are exagerated and freak her out so she won't let Kenshin near her. When he finally figures out the reason he goes to Megumi to confront her and gets the male version of the lesson, and then finally explains to kaoru they aren't life-like.
I remember the last but was karou convinced they were only allowed to have sex three times a week, and kenshin was like 'time to prove her wrong', lol
I think it was only a few chapters long, but it was complete.
Any help would be great, thanks!