nakereba ikenai なければいけない

Predicative phrase (expressing obligation imposed by the speaker) meaning: (you) must.

Nakereba is the ba-form of the negative adjective nai. It may be replaced with nakutewa, nai to, or the informal nakya.

1. After the stem of nai-form of verb
もっと勉強しなければいけません。
Motto benkyou shinakereba ikemasen.
You must study harder.
「私も行かなければいけませんか。」「いいえ、結構です。」
''Watashi mo ikanakereba ikemasen ka.''Iie, kekkou desu.''
''Do I have to go, too?'' ''No, you don't need to.''

2. After ku-form of adjective
もっと軽くなければいけません。
Motto karuku nakereba ikemasen.
It needs to be lighter.

3. After (adjectival) noun + de
You must be kind to old people.
Roujin ni shinsetsu de nakereba ikemasen.
老人に親切でなければいけません。

-> See also: nakereba naranai, nakutemo yoi