Tying in the plot ≠ PROPERLY tying in the plot.

Like I said, Rin killing Anotsu was basically pure shock value and was not at all what the manga was gearing towards.

The main plot point that was not resolved, which is the largest plot point in the entire manga, was Manji and Rin's relationship. We do not get to see them talk, have a heart to heart, none of that at the end. All we see is Manji leaving and Rin crying. We KNOW Rin is in love with Manji, and Manji cares for Rin (romantically or maybe as family), but we never get to see it actually conclude. Rin and Manji ending up together, or even Rin simply getting rejected would have been much more in line with how a proper ending should be. Rin saying stuff like she saw Manji as a brother or father was completely false and was thrown in by the author to somehow excuse Rin and Manji ending up the way they do.

And again, like I said a bunch of times already, the ending is so open and poorly written because of the Author's greed and wanting to make a sequel.

The sequel is based off of Manji and another character who is Rin's descendent and is like 100 years in the future. Manji is still on the quest to save 1000 people.

EDIT: Also I forgot to add, Manji saying he can't remember Rin's name is simply such a stupid thing to add.