Shunsuke is the older brother of Ayumi and Yuu.

Spoiler

In his first appearance during a future flashback in Episode 9, it is revealed that he has the power of Time Leap, but is limited to whether or not he is able to see with both eyes.

Spoiler

In the current timeline, he is blind. He tells Yuu and the others that every time he used his time leaping ability, his vision got progressively worse, until it finally blinded him completely. As a consequence, he is unable to use his powers anymore. Fortunately, Yuu is still able to steal the power to go back in time to save Ayumi.