nakucha なくちゃ

In Japanese, nakucha なくちゃ is normally used to say that you "must" do something. For example:

• ganbaranakucha
  頑張らなくちゃ
  [I] must word hard. Try my best. Put effort.
  • ganbaru 頑張る
    To work hard. Try your best. Etc.
• nigenakucha
  逃げなくちゃ
  [I] must run away.
  • nigeru 逃げる
    To run away.

Grammatically, it's a contraction of nakute wa なくては, which is the te-form of the i-adjective nai ない, "nonexistent," plus the wa は particle. See the article about ~te wa ～ては for details.

• Grammar
• Usage

Grammar

Basically, this ~te wa, or ~cha ～ちゃ, comes between a condition and a consequence. For example:

• okane ga nakucha komaru
  お金がなくちゃ困る
  Not having money: be troubled.
  [I'll] be troubled if [I] don't have money.
  [I'll] be troubled if [you] don't have money. (to pay me, for example.)

The nai ない can act as an auxiliary turning the verb into negative. In this case, nakucha often comes before dame ダメ, "no good," ikenai いけない, "can't go," or naranai ならない, "won't be," in order to say the consequence is bad. To elaborate:

• benkyou shinakucha dame
  勉強しなくちゃダメ
  To not study: no good.
  To not study is bad.
  [It's] bad if [I] don't study.
  If [I] don't study, [it'll] be bad.
  • Therefore, to study is good.
  • I must study. I should study. I have to study. And so on.
• benkyou shinakucha ikenai
  勉強しなくちゃいけない
  (same meaning.)
• benkyou shinakucha naranai
  勉強しなくちゃならない
  (same meaning.)

In other words, the phrases nakucha dame, nakucha ikenai, nakucha naranai, are double negatives. They say "not doing something is not good," so "doing something is good." This is particularly confusing since the thing that comes after nakucha can be omitted.

• benkyou shinakucha
  勉強しなくちゃ
  If [I] don't study.
  (incomplete sentence.)
  
  • What? What happens then?
  • WHAT HAPPENS IF YOU DON'T STUDY???
  • Tell me!!!

The phrase above implies that the speaker must study, or maybe the speaker is noting that someone else must study. Anyway, the point is studying must be done. But the phrase doesn't literally say that.

• chanto kangaenakucha
  ちゃんと考えなくちゃ
  If [you] don't think [about it] properly. (it's no good.)
  [You] gotta think [about it] properly..

Usage

In anime, characters that use this kind of contraction tend to be the cutesy ones, compared to those that wouldn't use this contraction, which would be the more serious ones. For example:

Manga: Machikado Mazoku まちカドまぞく (Volume 1, Page 20, まちのひみつ)

• {o-hazukashii} no dakedo
  uchi no ie
  iro-iro wake atte...
  お恥ずかしいのだけどうちの家色々わけあって･･･
  [It's] something {embarrassing}, but, in my [family] a lot stuff happened and...
  • iro-iro wake aru
    色々訳ある
    There are various reasons [for something to occur].
    A lot of stuff happen [that lead to other stuff happening].
• {kono tsuno ga haete-kitara
  mahou shoujo wo sagashite
  buchi-korogasanakucha
  ikenai} sadame rashii desu
  このツノが生えてきたら魔法少女を探してぶちころがさなくちゃいけないさだめらしいです
  It seems there's a rule [that] {as these horns sprouted out, if [I] don't search for magical girls and murderize them, that can't go}.
  • i.e. I must search for magical girls and murderize them.
  • sadame
    定め
    A rule that's been stipulated. (from sadameru 定める, "to stipulate a rule.")
    This noun is qualified by a very long {relative clause}.
  • buchi
    ぶち
    To hit. To strike. (verb.)
    Emphasizes force. (auxiliary verb.)
  • korogasu
    転がす
    To make something roll over. Trip over. To throw someone down.
    (not to be confused with korosu 殺す, which means "to kill.")
  • So buchi-korogasu means literally to throw down with force, which sounds practically like buchi-korosu, "to murder with force."
  • rashii
    らしい
    It seems. I heard. (of said rule.)