(slang) Alternative form of 彼氏 (kareshi, “boyfriend”)

historian

(Internet slang, especially anime and manga fandom) events or things from the past which one wants to whitewash/erase from history (due to it being embarrassing, poorly received, etc.); dark past

study of history

historicism

oral history

historic, historical / already-happened, past / former, old, traditional

researcher

a laboratory

research association; research society / group of enthusiasts (as may be found in schools, colleges, etc)