Dorm head of the Half-Blood faction, and their most powerful member in OLYMPUS. Person of unknown gender, whose powers are second to none. Can kill Servants on his/her own, and amongst the currently active Masters, without a doubt, the most powerful. Owns a Noble Phantasm of his/her own that is a family heirloom passed down to him/her, as he/she is of regal lineage, or so it is rumored. Forms a perfect pair with Saver during battle, and he/she is said to be absolutely merciless whenever challenged for his/her position as the Number 2.
It is said that facing Mori Kaoru spells a certain doom upon you, and if you managed to make him/her fight seriously, there is no going back. All the tales and rumors about this person mingle into one, and finding the truth about the scope of Kaoru's power is almost impossible at this point. However, for those who want to rise to the very top, and issue the challenge to the most powerful Master in OLYMPUS, this is a challenge they have to overcome.
Among all the Dorm Heads, it is said that Kaoru possesses the best balance of capabilities.