We did this specifically because we don't want people to think there is a Normal difficulty. And if you look at the enemy descriptions on the difficulty select, it goes Easiest, Easier, Harder, Hardest. We want the player to actually make a conscious decision on which difficulty to use instead of thinking there's a default.
Do you dislike combat in RPGs and want to breeze through as fast as possible? Pick Tourist.
Do you like combat but don't want to get stuck? Pick Agent.
Do you like combat and want want a challenge but don't want to agonize over every little decision? Pick Heroine.
Do you like combat and want to really dig deep into the systems and find the perfect strategies? Pick Super-Spy.
I'm personally spending the most time on Super-Spy difficulty because as the person who designed the systems, I find it the most fun (plus I gotta make sure that it's beatable).
...