18+ Pajama na Kanojo.

Keisuke and Makura are childhood friends who grew up together almost like brother and sister. One day, due to a misunderstanding they had, Makura left the house angry until Keisuke's Mom is worried about Makura not coming home yet, thus Keisuke is told to go look for her.

Reluctantly, Keisuke went out to find Makura, He ended up at a place they used to go often, the sunflower field. Luckily, Makura was there. Keisuke joined her sitting on the bench and they began to reminiscence.

When Keisuke decided that they should head back home, he phoned her mom to say that he found Makura, only to be shocked when her mom told him in panic to head to the hospital. At that same moment, he looked at Makura, who was not standing but floating in the air...

(Source: Pinoymanga Scans)