Kotei No Himawari summary:

A nostalgic fantasy that takes you to the "past" at the bottom of the lake.Summer...Aohata Village, which had sunk to the bottom of the lake due to an abnormal drought, has come back to life.Takuro, a native of the village, remembers his friends who went missing in the village and heads for the lake. However, when he passes through a field of sunflowers that appears before his eyes, he finds himself in 1995, just before the village was abandoned...!