Rui is a young boy with amber eyes and light brown hair, which was most likely inherited from his mother, Misaki Ayuzawa.
Rui is a very quite and gentle boy, he often gets botherd by his sisters wild behavior but tags along with Sara anyways and often yells at her when she gets too excited or does unnecessary things. Rui also seems to adore his family and is close to them than others.
Like his mother, Misaki, he often gets frustrated by Sara. And like his father, Takumi, he is often very quiet and tries to stay out of trouble.
Throughout the beginning of the oneshot it is hinted that Rui studied and lived overseas in Britain and is currently now in Japan, Kyoto with his family.
Takumi Usui is the father of Rui Usui.
Misaki Ayuzawa is the mother of Rui Usui.
Sara Usui is the older sister of Rui Usui. Even though Sara always teases him and tires him out, he stays with her most of the times and tags along with her.