Kimi to ita mirai no tame ni 'I'll be Back'

On the last night of 1999, 22 year-old Atsushi Horigami suffers a heart attack and dies during the year-end countdown. In the next moment, he awakens alive and well in his own room - but the year is 1995, and he is 18 years old again, though with all memories up until the eve of his "death" in 1999 intact. Trapped in a never-ending loop, Atsushi is forced to re-live the same four-year period over and over again until he encounters two others also experiencing the same phenomenon, one of whom is already going insane...