Understanding んだから at the end of a sentence


こうなったらお料理上手になって見返してやる **んだから** ！
とレーナは内心決意を固め、妙に気合の入った足取りで格納庫を歩く彼女に、シンが怪訝な顔になりつつ従う。

86─エイティシックス─Ep.4 ─アンダー・プレッシャー─ 安里アサト

Neither シン or レーナ is good at cooking but they are competing with each other to
get better at cooking.

Could you please explain the bold んだから at the end of this sentence (or an
imbedded clause, in this case)? I know when it’s used in the middle of a
sentence it means "because". But I’m not sure about this case.




Practically I think this is a usage which does not translate to _because_ very
well. It can be considered as a pattern for expressing a resolution: _Now, I
will be a good cook and 見返す (somebody)!_.

What is omitted after だから can be 覚えておきなさい/覚悟しなさい/見てなさい etc., but these don't
usually appear in this usage. Verbosely, _Now I will be a good cook and ..,
**so be prepared**!_. This _so_ corresponds to the だから.

As 見返す is used in this example, it implies that the speaker is in a 'lesser'
position, e.g. like being a bad cook in the example. Or someone thinks that
the resolution is unachievable. In other words, んだから construction implies that
the resolution has the nature of 'reversing' the situation or somebody's
expectation.

Also んだから is usually feminine. A masculine version would be perhaps やるからな
(…見返してやるからな).

