I want to post strategy guides for all the bosses, so here's one for Le Rauxe:
There's no definited strategy for this boss, but doing the following might help you:
When the fight starts, use pistol to buy time and then jump in front of the purple guy. Start beating on with your sword (here you should try to get the strikes on equal intervals, around half a second, so Le Rauxe will not be able to parry or return and you will be able to get more strikes in) If he hits you 1-2 times jump away and then repeat. Try to avoid making him use his jump, though it is not so nasty.