This is for killing the boss at the end of the tutorial when the screen goes dark and the alarms are on. It should be noted that your exp from normal play carries over here, even though you don't see it. First off is to get max xp through normal play,
When you pick up all 3 weapons in the tutorial, immediately press start and upgrade yourself with evade, jump, run, and some damage upgrades on the fire sword. This should make for an easy fight if you rush around, evade, and use the X, X, Y combo after his jump moves (you can throw 2-3 extra X hits in there without getting hit if you're lucky).
In an earlier version of the game you could salvage the other 2 weapons If you needed health, making it even easier, but that seems to be patched out now.