Very Easy Cast Haste and protect(Gambit set) you ought to get rid of Enkidu first but not to forget to steal from him. Then the next target you just slow him down by using decoy to lure him. But you have to steal part of genji equipment before you take him down in each time(but the key is required.) It may take some times to successfully steal from him,just be patient. Then,once again,if you defeated him, he will flee to another part of lhusu mine and even stronger.
p.s. It can be the perilous fight when he has enkidu with him. Remind of using bubble or equip bubble belt to everyone(except Vaan cuz he need to equip the accessory that increasing successful rate of stealing.