also: なんせ
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.
Since this is my first trip abroad, I'm nervous, you see.
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.
After all, I'm from the countryside, so I'm not used to city life.
Since it's been ten years, I'm worried whether I can speak well.
だって is a casual, often defensive 'because' typically used when answering a question, whereas なにせ is a set phrase for explaining a situation with a calmer, more explanatory tone.
なぜなら is a formal, logical connector meaning 'because' used mainly in writing, while なにせ is colloquial and often carries a nuance of 'after all, as you'd expect'.
Usually written in kana; the kanji spelling 何せ is rare.
Colloquial variant of なにせ, common in casual speech.
Kanji spelling is rarely used; kana is strongly preferred.
A shortened form of 何せよ, literally “whatever one does” or “in any case,” using the imperative of する. The colloquial variant なんせ developed by sound contraction.