No, I'm not talking about that TV show about Sam, Dean, and Castiel (though if you think about it, the fandom for that show probably has more man-kissing in it than the entirety of Boys Love/yaoi does as a genre) – today we're talking about supernatural- and fantasy-themed BL, both in visual novels and the genre more widely.
Magical elements in Boys Love stories are quite widespread, both specifically Japanese-flavoured folklore and elements drawn from other cultures. The fusion of the supernatural genre and BL makes for an appealing mix, as both often deal with extreme emotions and high stakes storylines.
It's easy to understand why titles which incorporate a supernatural or fantasy element into Boys Love manga, anime, live action or visual novels are so popular – BL and fantasy are both genres that many audience members use for escapism, and the dramatic potential of supernatural elements offers a broad variety of options for writers.
A very common trope in Japanese light novels, manga, and anime currently is isekai stories, where a character is transported to another, typically fantasy, world and forced to fend for themselves in strange surroundings. Naturally, there are Boys Love examples of this subgenre, such as the manga Ai wo Ataeru Kemono-tachi, which features a three-way gay marriage between the character from another world and two shapeshifters who can turn into animals.
The manga The Titan's Bride, later adapted into an anime of the same name, is another example of a Boys Love isekai fantasy – a high-school basketball player is summoned to a world of giants, where the prince asks for his hand in marriage.
When it comes to visual novels specifically, one example of supernatural BL with a traditional Japanese skew is Tokyo Onmyoji, which draws on concepts of ancient divination and exorcism to tell a story of magical beings causing harm to people and that must be stopped. It features four love interests.
Sorcerer's Choice: Angel or Demon? features a magic-user as its protagonist, caught between the forces of light and the forces of darkness. The Light route, apart from its bad endings, is a very soft and sweet romance, while the Darkness route is much spicier. It's the perfect entry-level game for someone who loves fantasy and supernatural elements in Boys Love but isn't especially familiar with visual novels.
The Night Beyond the Tricornered Window is a manga, anime, and live-action film that skews heavily into the horror and mystery end of supernatural Boys Love. Kosuke Mikado can see ghosts, and exorcist Rihito Hiyakawa wants to harness his powers – when they touch soul-to-soul, an intimacy that brings extreme pleasure to them both, their supernatural powers are amplified. If you're looking for something creepy that's heavy on the innuendo, check this one out.
Outside of Japan, other gay male fantasy romance includes xianxia danmei from China, such as Mo Dao Zu Shi and Heaven Official's Blessing, both by author Mo Xiang Tong Xiu and both translated into English in their original novel form as well as comics, cartoons, and a live action series in the case of Mo Dao Zu Shi – though, it should be noted, censorship has led to these adaptations turning the canonical romance of the original novels into subtext.
In many of the above cases, the romance of the Boys Love story is intrinsically tied to the supernatural elements on display. This allows the creators to explore themes that more realistic stories wouldn't allow for, as the imagination can play a larger role.
There are many highly popular BL stories which incorporate fantasy or supernatural elements into their narrative – this is just a small taste of what you'll find out there. They vary in tone and content as much as BL does as a wider genre, and offer something for every taste.