How to say "fanatic" in Japanese

• 基地きちJLPT N2approx.Common
  noun (suffix)Covers an obsessive enthusiast or fanatic in a jocular, humorous way; an internet slang term. Use when teasing someone playfully about their consuming hobby or fandom, not in serious or formal contexts.
• 信者しんじゃJLPT N1approx.Common
  nounMatches the colloquial 'fanboy' sense of fanatic: someone uncritically devoted to a person, brand, or hobby. Fits everyday conversational talk about superfans whose loyalty borders on blind faith.
• キチガイCommon
  noun, noun (suffix)A sensitive word whose core senses are mania, craze, and obsession; it is seldom the word you want for 'fanatic'. Avoid it unless you fully understand its offensive potential; safer alternatives exist for enthusiast.

For a devoted enthusiast use 基地 or 信者 depending on whether you want jocular internet flavor or a colloquial 'fanboy' tone; 「キチガイ」 is a sensitive word really meaning mania or obsession, rarely advisable.

Usage comparisons are AI-assisted and cross-checked by multiple models; for study reference only

• ファナティックfanatic
• 狂信者きょうしんしゃfanatic
• 熱狂的信者ねっきょうてきしんじゃfanatic
• 狂信的きょうしんてきfanatic
• 狂的きょうてきinsane
• キチenthusiast
• 儲しんじゃfanboy
• 凝固まりこりかたまりcoagulation
• 基地きちenthusiast
• 信者しんじゃfanboy
• きちがいmania
• 狂いくるいfanaticism