Talk:Android 18 VS Captain Marvel/@comment-30976814-20170525045750/@comment-4970402-20170525054147

As they described in their rundown of Superman vs Goku (meaning this is how they interpret Ki to work), Ki is a physical manifestation of one's fighting spirit, a life energy of sorts.

According to Akira Toriyama, "ki is made up of multiple components, including: Genki (元気; lit. "Energy"), Yūki (勇気; lit. "Courage") and Shōki (正気; lit. "Mind")."

Though Dragon Ball makes the clear destinction that Ki is not magic, it is still very much mystical in nature. A quick google search tells me Carol "cannot absorb magical energy without consequence", so while it is very likely she will be able to absorb 18's attacks there may be negative side effects to doing so.