eccentric young man; oddball guy
Casual, often affectionate term for a young man who is quirky, unconventional, or hard to understand. Compare 不思議ちゃん for females.
See also: 不思議ちゃん
He's the class oddball, always making off-the-wall remarks.
That eccentric guy suddenly starts talking about philosophy, which is interesting.
Refers to an eccentric young woman; 不思議くん is the male counterpart.
Common casual spelling using くん in kana.
Kanji spelling for くん; less common but seen.
From 不思議 (mysterious, strange) + くん (familiar suffix for males). The exact origin is uncertain, but it likely emerged as casual slang to describe quirky young men.