As one can see from http://mondaiji.wikia.com/wiki/Sakamaki_Izayoi , he has gained
Sun Authority: Leo: A Sun Authority stated to be the power of the Fifth Western Zodiac, Leo. Leo's power is based on the myth of the Nemean Lion, a beast who was completely impenetrable to blades. This protection was grated to Izayoi and blessed him with the same defense against blades, thus making it possible for Izayoi to safely catch the Spear of Indra and throw it back. In Last Embryo 1, the Minotaur attacked Izayoi with Proto Keravnos but he was completely unharmed despite that a single strike from Proto Keravnos can surpass the concept of "slash". However, this Sun Authority is not effective against Gifts which could break the Gifts of stars or slay the Celestial Spirits, as seen in volume 12 when Laius successfully slashed Izayoi by his Harpe, though Izayoi weakened his attack and only received a small injury.
Who gave him the sun authority and when did it happen?
