Nanashi (Japanese: ナナシ roughly meaning nameless) makes his appearance in Slayers: Knight of Aqua Lord. He refuses to disclose his real name, which he claims to have discarded.
He is a master swordsman who becomes Lyos' mentor to train him into mastering his powers to become a fully-fledged Knight of Aqualord. Long before his relation with Lyos, Nanashi was friends with the former Knight of Aqualord who perished while saving him from mazoku. He used to be a priest and a theological scholar at Orun's smithing village where he developed a profound understanding of the power of the gods,
He shows up later in the series and takes a keen interest in Lyos, or rather the power of the Aqualord inside of him. He takes Lyos away and trains him. Lyos was uncertain of him at first, but eventually develops a thirst of becoming stronger and controlling his power. In a short span of time the two become close as master and student.
In battle, Nanashi is a formidable foe who is even capable of taking on a high-ranking mazoku general in a straight-up swordfight. He reaches incredible speed and maintains accuracy and strength in his strikes. As a former priest, he is also able to call upon the power of the gods to launch devastating attacks. However, his mortal limitations eventually catch up to him and he struggles to keep up with such an opponent once the latter begins to unleash the true extent of their power.
Nanashi appears to be a wise and knowledgeable individual. He remains consistently composed and level-headed; proof of his maturity. He thinks rationally and usually cuts to the chase by wanting to be forthright which can make him seem cold and coarse. However, towards the end, he unravels a much more understanding and somewhat tender side to him, especially towards Lyos.