Rot Technique Maximum: Wing King manipulates the user's blood and shapes it into large wasp-like wings. These wings can be used to create vector lines made of blood which can be used for offensive purposes or to increase the user's maneuverability. When the lines of blood connect with their target, they're instantly burned by the corrosive effects of the blood.
Eso used this technique to begin his fight with Yuji and Nobara. By activating it, Yuji was forced to flee and managed to move faster than Eso's lines of blood could. However, Eso was eventually able to catch up and hit Nobara from behind, badly burning her left arm.
Once forced to deactivate Decay, Eso immediately switched back to utilizing Wing King. He momentarily forced Yuji back before being injured by the sorcerer's Black Flash attack. While badly injured, Eso was unable to utilize Wing King.