Furries / Yiffing
Furry fandom centers on anthropomorphic animal characters — creatures with human traits — and 'fursonas,' the personal animal-persona many fans create. For most, being a furry is a social and creative hobby, not inherently sexual. The erotic side, nicknamed 'yiffing,' is sexual activity or content within that world: roleplay, art, or sex in or around fursuits (the head-to-toe costumes) as one's animal character. Interests span cartoonish woodland creatures to invented species. Only a subset of the fandom is about the sexual angle at all.
The appeal blends creative self-expression — becoming a character that feels truer or freer than everyday self — with community and, for some, the playful eroticism of animal personas. Costumes and anonymity can also lower inhibitions and add fantasy.
Partners take on their fursonas — through art, text roleplay, playful animal behaviour, or (for some) partial or full fursuits — and interact or have sex in-character. Much of it happens online through writing and commissioned art as much as in person.
Low physical risk. Fursuits get very hot and limit vision and airflow, so take breaks, hydrate, and don't overheat; clean costumes well, especially after sexual use. As with any roleplay, negotiate characters and limits first.
It's worth separating the fandom (a broad, largely non-sexual creative community) from 'yiff' (its explicitly sexual corner). Full fursuits are expensive and often not used for sex at all; much yiff play is roleplay, art, or persona-based rather than costume-based.