also: なんせ
adverb
in any case; anyway; after all; you see
Used to introduce a reason or explanation, often with a nuance of 'after all' or 'you know'. Can also emphasize a point, similar to 'particularly' or 'especially'. The colloquial form なんせ is common in spoken Japanese.
なにせ初めての海外旅行だから、緊張している。
After all, it's my first trip abroad, so I'm nervous.
なんせ相手はプロだから、勝つのは難しい。
Anyway, the opponent is a pro, so it's hard to win.
なにせ彼は忙しい人なので、連絡が遅れても仕方ない。
You see, he's a busy person, so it can't be helped if his reply is late.
Kanji spelling is rarely used; kana is strongly preferred.
Derived from 何 (nani, 'what') + せ (se, imperative form of する, 'do'), literally 'do what'. The original meaning shifted to 'no matter what' and then to the current adverbial use. The colloquial form なんせ is a contraction.