There's also 'RWBY and Touhou: A Magical Encounter'. In this fanfiction, the magical elements of Touhou are blended really well with the world of RWBY. It shows how the RWBY characters react to the strange and powerful magic from the Touhou universe. It's a great read for those who like to see different fictional universes collide.
Another theme is cultural exchange. The RWBY world has its own set of values, cultures, and technologies, and Touhou has its own very distinct world of youkai and magic. Fanfictions often show how the characters from each world learn about and adapt to the other's culture. For example, a RWBY character might be fascinated by the way magic is used in Touhou. It can be really interesting to see how they incorporate elements of each other's worlds into their own understanding. And this can also lead to some character growth as they expand their perspectives.
One great 'Dark Souls Touhou crossover fanfiction' is 'The Gensokyo of Lothric'. It combines the dark and challenging world of Dark Souls with the colorful and magical world of Touhou. The characters from both universes interact in really interesting ways, like Reimu facing off against some of the Dark Souls bosses. Another one is 'Touhou in the Abyss' which has a unique take on how the Touhou characters would fare in the abyss - like Marisa using her magic to navigate the dangerous terrains.
One popular 'touhou crossover fanfiction' is the one that crosses over with 'Pokemon'. It's really cool to see the characters from Touhou in the Pokemon world, with unique storylines like Reimu becoming a Pokemon trainer. Another great one is the crossover with 'Final Fantasy'. The magic systems of both get intertwined in interesting ways.
There's a crossover fic called 'Colors of Combat'. In this story, the Reds and Blues find themselves in the RWBY universe and have to adapt to the new rules and powers there. It has great character development as they learn from the RWBY characters and vice versa. The story also has some really cool fight scenes that blend the combat styles of both series.
Perhaps 'Touhou in the Underground: A Crossover Fanfic' would work well. It gives a sense of the Touhou characters being in the Undertale setting.
In 'touhou crossover fanfiction', adaptation is a big theme. The Touhou characters need to adapt to the new environments of the crossover universes. Whether it's a high - tech sci - fi world or a medieval fantasy land, they have to learn new skills or use their existing ones in different ways. Additionally, mystery is often present as the characters try to figure out the secrets of the new world they've entered.
Well, 'RWBY x Harry Potter: Magic and Dust' is also a very good one. In this fanfic, it imagines what would happen if the RWBY characters entered the wizarding world of Harry Potter. It's full of creative crossovers, like Ruby using her scythe in Hogwarts, and the story has a great plot that keeps you reading.
Character development is key too. When RWBY characters meet characters from another universe, like in a RWBY and DC Comics crossover, they should grow and change in response to the new situations and characters they encounter. This could be Weiss learning new ways of combat from Batman or something like that. Also, a good plot that doesn't simply rely on the novelty of the crossover but actually tells a great story is very important. It should have conflict, resolution, and keep the reader interested throughout.
There's also 'RWBY and Halo: A Crossover of Worlds'. In this fanfiction, the Forerunners from Halo are somehow connected to the Dust in RWBY. It's really interesting how the author weaves together the two different mythologies. It has some great character interactions, like Ruby meeting Master Chief and their initial confusion and then mutual respect.
One popular SCP RWBY crossover fanfiction is 'SCP - RWBY: A Cursed World'. It combines the dark and mysterious elements of the SCP universe with the colorful and action - packed world of RWBY in an interesting way. The characters from RWBY often find themselves in situations where they have to deal with the strange and dangerous anomalies from the SCP world, which makes for some exciting and unexpected plot twists.