Touhou Game Club

Show them one example of the earliest Touhou Windows, like EoSD or PCB. PoFV is fine too since it's all about being competitive. You may as well show them how to play it, and explain what's Touhou exactly ? It's okay if you are gonna prioritize both 12.3 and DoTS, but you need to always remember their roots. Don't ever give an impression that Touhou is basically a fighting game, or worse, an anime.

There goes the basic part.
Additionally, you can also show them some of fan-games goodness, such as Genius of Sappheiros, Touhou Sky Arena, Touhou Labyrinth, Sanae Challenge Fusion, Touhou Pocket Wars EVOplus, Touhouvania, Paper Tenko, and etc. The point is to get most of available genres covered. With this, you can tickle most of gamers' interest. As we all know, there are several different layers of gamers with different preferences, you need to attract as many as possible to gain the best result.

If you think it's necessary, you can also provide some fan-made videos. My #1 recommendation is obviously Kinemakan's. While most are only alternative interpretations, they are still good enough to show Gensokyo, its inhabitants, and their relation.
Don't forget to teach them about fanon and canon as well. Nothing is worse than a self-proclaimed fan with no basic proper knowledge.

Show them that even though Touhou is basically a vertical bullet hell shooter game, there are actually many ways to enjoy it.