I just saw the posting by Okko Sweet Romance for a special contest for their Rental Boyfriend otome. If you win, they'll publish your idea as one of their gacha short stories and also give you free points (platinum) for the specialty items that usually cost real money. All you have to do is write a special scenario, Christmas theme, for the MC and one of the guys from the otome. 700 words max and submit it by December 6th. Submit submissions (preferably Mword) to firstname.lastname@example.org with appropriate headers.
For more info, download the app and play through one of the guy's route to get a sense of their personalities. You can submit routes for as many as you like. I don't think I'll be doing this due to lack of time, but I'll definitely keep it in mind. It would be really fun to win though, wouldn't it? Your idea published to thousands! Anyhow, download the app if you want more info. It only takes about a minute.