Damn, last arc was really disappointing. Imamura leaping through time... then againing again. It became a clusterfuck. As someone commented before, the first arc itself was godly, but the 'I want to die' musical arc is pretty good too. I guess the author didn't want to bother too much with time travel logic and left an open end?
Could anyone clarify the timelines if they got a grasp? Did danchou really get pregnant? I remember that in one of the chapters she's dreaming about this timeline, and does especially say there is no kid Chankuma.
But still it was a pretty good high school drama manga series, if not for the last arc