1. if (it) doesn't exist, if there is no ..., if (one) doesn't have ...

expressions (phrases, clauses, etc.) colloquial word usually written using kana alone

2. if not ..., unless ...

auxiliary expressions (phrases, clauses, etc.) colloquial word usually written using kana alone

必须……

3. have to ..., must ...

expressions (phrases, clauses, etc.) auxiliary colloquial abbreviation word usually written using kana alone

逮捕された時はどう思いましたか？ 反省しなきゃいけないかな、後悔はある。

被捕时你是什么感受？ 或许需要反省，确实有些后悔。