In this video, the characters are saying the lines they had in the game, only reworded, but they basically mean the same thing.
やってみせる、それで自分が取り戻せるなら。
In the video game, there is a line of text:
自分自身を取り戻せるなら、やってみせるさ。
"If it will make me myself again, I'll do whatever it takes."
Which I'll assume says just about the same thing as the video, just reworded. Both lines are spoken by the same character. But I've always been confused about the それで since all it says in the dictionaries for それで is
- and; thereupon; because of that