Kei X Yaku has plenty of promise. The central concept is great and there were some very fun moments. I also really liked the art style. 

Unfortunately I felt that this manga didn't quite live up to its potential. The plot was enjoyable at the time but wasn't very memorable.  I also didn't feel that I had a real grasp of the personalities of either of the main characters, which made it hard to really care about them. 

This is only volume one and so I'm hopeful that future books in the series will improve on this one, and I do recommend giving this a go.