Helvius Cecia, a member of the Thieves Guild, can be found in his Bruma home and is the Master Hand to Hand Trainer. You must get a Master Training reference from Davela Hlaren and Ra'qanar before he will teach you. He is available 6AM-6PM every day except 8AM-10AM Sundas. To recieve training from Helvius Cecia you must attack him with your fist. If you take out a weapon whilst fighting him, He will call the fight off.