Othi-chan has almighty omnipotence. All possibilities are within reach for Othi-chan. That means that all successes and failures are possible. Hence the 50%.
http://41.media.tumblr.com/cad7c418a707ba237c7b9fe1d67f90b2/tumblr_n646e2ZZ1f1sje6kuo1_1280.png here you go another excellent image of the best girl in toaru