You have to use triggers for that. In modmaker, click on tori head, then Body II tab, then check "enable trigger system". Then, put it in some group (like 1) and make it collide with some other group (like 2). For trigger action, check Uke, because you want Uke to win if tori's head gets hit. Afterwards do the same for Uke's head except under trigger action check "You" instead of "Uke". Now, put triggers on your blade tips also. Click on each of them, put it in group 2, and make it collide with 1. Leave "trigger action" as none.

You could also make it so that your own blade hitting your head doesn't cause insta-loss, but you need to put blade tips in seperate groups and make heads collide with the group of opponent's blade.