Date a Live, Vol. 4 (Light Novel): Sister Itsuka, Paperback

Shido was going to save Kurumi and Mana. He had to. And yet in this critical moment, he finds himself immobilized, unable to follow through on his promise. If Kotori Itsuka hadn't shown up at the last second, everything would have fallen to ruin...but Shido still feels like his world has come crashing down as he finds out his little sister is a Spirit, too...