He has curly hair the color of green tea, which he keeps relatively short, a small patch at the base of his head completely shaved, with two short ahoges sprouting from the top of his head. He has a few longer clumps of hair hanging down in front of his left ear and between his eyes, and long bangs that cover the majority of his forehead, side-swept so as not to impair his vision. His eyes are green, and they slope downwards towards the sides of his face, both framed by notably long, thick eyelashes.

He wears a dark blue striped sweater with wide, elbow-length sleeves, a small chain accessory pinned on just beside his right shoulder. Underneath this, he wears a darker shirt that pokes out from below the hem of his sweater and from above its low-dip collar, still leaving his collarbone exposed, and another white garment that hangs out of the bottom. He also wears baggy, light-brown sarouel pants, and navy-blue slip-on shoes with white soles.

Rantaro wears a necklace with a rectangular crystal pendulum hanging at the end of it, a silver bracelet on his right wrist and a different, larger, dark brown bracelet on his left that wraps around his wrist several times. He has multiple silver rings: one on his left index finger, one on his right thumb, and one on his right index finger, and on his right middle finger he wears one longer and darker ring. His right ear has five ringed cartilage piercings, and he wears a small beaded earring in the lobe of each ear. He wears a bracelet that matches with Korekiyo Shinguji, it has army green, black, and red beads. In the middle it has Korekiyo’s initials, K.S. and a green tea ball bead in the middle of the K and S.

Rantaro is a carefree and relaxed person. Despite his mysteriousness, he is described as one of the more ordinary students, with he himself stating that he can sometimes get a bit overwhelmed by the others' stranger personalities. Nevertheless, he is shown to have more patience than others with some eccentric students, having a tendency to just laugh off some of the potentially hurtful things they say. He is usually seen smiling and describes himself as "not a suspicious guy,". He gives off a really calm and composed vibe.