Yukihiro Smith is Tatsuki's classmate and friend. He approaches Tatsuki on his way home after the tiger event, believing Tatsuki to be an extraordinary fighter and asks to be his student in-training. Tatsuki agrees to his proposal, despite knowing it was Misaki who was the one to defeat the tiger. Yukihiro is described as being "a good six inches shorter" than Tatsuki and looked "too young" to be a senior in his class.
With a bubbly, optimistic outlook, Yukihiro is an active and kind soul. Despite having grown up with an autistic younger brother and dealing with his parents' divorce, Yukihiro is Tatsuki's positive motivation to achieve big; and ultimately he is the one who convinces Tatsuki to accept being a Ryuu (unknowingly). Yukihiro has a fascination with nature, which proves to be one of the reasons Misaki falls in love with him, and dreams to be a real hero for his younger brother.
Yukihiro is not capable of seeing Misaki, as he is a regular human, but later becomes a part of the trio to stop the Tigers from killing Tatsuki and wreaking havoc in the world. He reciprocates Misaki's feelings for him, but does not advance the relationship any farther. He does, however, complain to Tatsuki about an unnamed girl he is smitten with who he cannot summon the courage to confess his love for. Tatsuki, speaking from his experience with Natalia, says to neither do anything or wait, instead focus on himself before dealing with love.
Art by @Fallen-Illusionist on DA.