I can't remember the title but I remember several details about the manga.

The ghost of a dead high school girl travels back in the past to meet a boy classmate. He sees the ghost and the living girl at the same time. Then the boy put two and two together and realized that she will die in the next few months. The ghost sleeps then wakes up from a nightmare, speaking the name of a fellow school girl who was believed to have committed suicide. The boy surmised that the ghost girl was murdered. He also believes her murder is related to the suicide of the fellow school girl

Can anyone please tell me the title?

Might be this one
https://www.mangaupdates.com/series.html?id=126275

Yes, you're worthy!

You are correct. Thank you very much.

Kimi ga Shinu Natsu ni