The butterfly effect in full motion.
What They Say:
On August 20th, on his way to delivering Mayoi what she had forgotten at his home, Koyomi encounters Yotsugi Ononoki, a familiar girl. Koyomi spends the day buying Yotsugi ice cream instead of doing what he originally planned to do. Unable to find Mayoi, Koyomi gives up and heads home and realizes that he has not done any of his summer assignments, even though tomorrow was the first day of school. With help from Shinobu, Koyomi travels back to the past so that he can finish them, but instead, they end up traveling back 11 years ago!