Waifu

Waifu is fandom slang for a female character someone has claimed as a favourite. The tone ranges from a passing joke to something the speaker actually means, and both readings are usually available at once. The word applies to fictional characters and only to them, which is the part that makes it funny and the part that makes it uncomfortable, depending on the room.

The origin is a single line. In Azumanga Daioh, the teacher Kimura is a running joke about a man who should not be near a school, and in one scene he holds up a photograph and says my wife in English, with an accent that fan subtitles rendered as mai waifu. Fandom kept the spelling and dropped the context.

From there it spread through image boards and then into official-adjacent use: character polls, merchandise marketing, mobile games built entirely around collecting characters. Japanese fandom has its own vocabulary for the same feeling, including oshi for the character or performer you support. Waifu stayed the English-speaking version, borrowed from Japanese and aimed back at Japanese media.