Actually we allow all romantic-themed games in general, not just limited to strict simulations and visual novels. So whatever you feel you can create and add to your itch.io page (even comics!), go for it!
The jam spans for the entire month of June, with some leeway in submissions running until the 4th of July. You can work on planning your game before the designated month but no production should be done until June starts! Teams and solo entries are totally acceptable.
Ren'Py - Visual novel engine of choice for a lot of Western developers. Uses Python programming language to create its games.
TyranoBuilder - A visual scripting program for VNs that can be found on Steam. Good for smaller projects or for those not comfortable with straight up programming.
Twine - A very accessible interactive storytelling tool (I find this tutorial to be a good introduction to even the most beginner). Can upload your story to be playable via simple HTML. You can even use add-ons for it such as this one to emulate text messaging.
...or whatever you feel comfortable creating in! Go ahead and check out the games for the prior years of the jam for ideas, too!
FAQs (I'll be answering some questions here as I get them):
Are comics allowed? Itch.io has been getting a lot more comic uploads lately and because of that I say GO FOR IT! Make a romantic comic in the month of June if you wanna do that route.