ソレノナ

A week before summer vacations. Main character loves to spend time on the school roof with just the wind and the sun making him company. One day he goes there as usual and meets another male student. He is given student notebook that he never dropped. Surrounding reality starts to get distorted. It's an ambiguous state that can be described as a dream. There is something that he has not noticed yet.

[From vndbreview]