[@Indrajita]Isekai magic, I guess lol

For MacKensie, her powers are hyper agility and acrobatics. Also her already Olympic level marskmenship is enchanced, so it can mostly be reasoned out with instinct in a dangerous situation.  Her body is just reacting and she's discovering it all post-hoc.

It seems Arthur is in a similar boat (lol boat... he's a sailor) with his abilities, though I can't speak for him.

Adam discovered his plant manipulation by accident right at the start of the story.

Makes sense to me, as far as fantasy stories go :P