Deed
noun
You go for the sake of others. You are constantly doing deeds like this for others.
こうい
This is a jukugo word that uses the on'yomi readings of the kanji. You should be able to read this on your own.
私がそのような残虐行為を繰り返したのは、その度に達成感を得られることができたからです。
I repeated those brutal acts because I was able to feel a sense of accomplishment each time.