Hikaru is a boy in his mid teens; he can been slowly maturing as the manga goes on. He has a thin figure and dark spiky hair.
Hikaru is a friendly and open boy. At the very start of the manga it is hinted that he may have had a attraction to his older sister, however this is soon dropped. When he was younger he was apparently prone to being easily frightened and wet himself an embarrassingly large number of times. He is shown to be very mature for his age, to the extent it even shocked Jun.
Hikaru is first seen waking up his sister after she had overslept for a meeting at her school. Later after she had been attacked by the Devilbeasts and become the Devilman Lady, Hikaru tries to comfort Jun saying that what she did was incredible and that she saved as many as she possibly could, leaving Jun feeling guilty about not telling him the truth of what really happened.