Fight against the enemey with 戦う

Vocabulary Explanation:

Luna explains that Usagi must become Sailormoon to fight against enemies. Upon transforming, Sailormoon discovers the opponent has targeted her friend Naru. When Sailormoon arrives to help, the enemy sends mind-controlled people to attack and harm her.

ルナ:: 「戦(たたか)うのよ！　あいつをやっつけんのよ」; “Fight! You have to take that one down!”
セーラームーン:: 「ええっ？！　何(なん)で！？　どうやって！？」; “Ehh?! Why?! How?!”

Key Points

1戦う here is a real battle, not a friendly contest

Luna is ordering Usagi to fight the enemy directly. Among common competition vocabulary words, 戦(たたか)う is the most adversarial, and this scene shows its core meaning of battling an opponent.

2のよ turns a statement into a firm command

戦(たたか)うのよ！ is grammatically a statement, but ending it with の plus よ delivers it as an emphatic directive, like saying “you are going to fight”.

3やっつけんの is a spoken contraction of やっつけるの

The る of やっつける collapses into ん before の.
やっつける means to beat or finish off an opponent, and あいつ is a rough, distancing way to say “that one”.

4何(なん)で and どうやって stack two protests

何(なん)で asks “why” and どうやって asks “how”. Firing both off after ええっ？！ shows Usagi has no idea why she should be the one to fight or how she is even supposed to do it.