This post is outdated and I'm too lazy to update it.
1. If that's what happens during sage battlefield,don't get surprised,for some reason, there isn't that much time to select ninjutsu like arena and normal fights,so however clicks 1st goes 1st, If u and the enemy click around the same time,then depending on ur initiative and position you go 1st.
2. If you're talking about arena, then u must've activated u're ninjutsu a bit late after he did, cause if u activate u're mystery before his starts (meaning it's already been selected) by 1 second or though,then he'll go 1st.