if it's traumatic/terrible/standard shb bullshit you want, i can offer something that happened to rhus after the siege on lakeland by eulmore, that level 76 solo duty. he dated an oc i made up for his story, a drahn in the crystarium guard who got turned into a sin eater during the attack and during the clean-up after, rhus had to mercy-kill him.

if it's sad bullshit, i can give the level 70 drk fight.

otherwise, maybe the time he got his scar and why he wears an eyepatch all the time