Couple of things worth noting:
On pg. 10 Yuuma sees a vision of a Mother and Child which is gone in the next page panel.
You can see the same book Yuuma was reading in the library "The Afterlife" now sits on Hina's bookshelf.
The framing of Hina's bedroom mirrors Yuuma's (bed on the left/door on the right vs. the opposite for Yuuma).
Hina is wearing the same Dark Star-decorated shirt Yuuma would often be seen in (first appearance in Ch. 19 and last in 97).
Hina also has a stuffed doll (in this case a rabbit) like Yuuma's horse plushie Umakin.
She has the same 100-day calendar on her wall now.
Ch. 1 begins fading from black with Yuuma switching on his desk lamp while Ch. 100 ends back to black as Hina switches her's off.
Overall, this was a truly masterful 10/10 work.
Not too many mangas that were structured to be long-runners from the start (and escaping the Axe) managed to stick the landing by the end, and even fewer within the horror genre. There were no M. Night Shymalan tweeeests, no sudden deus ex machinas, everything that happened across the story logically fed into the conclusion in a natural and convincing manner. The author was able to craft a very compelling meta-plot while dedicating only a few pages out of each chapter towards it and yet maintained great pacing without stalling or jumping ahead (the days being X'd out on Yuuma's calendar in the background of each chapter were steadily marking off the time remaining). This was an excellently planned series.
The stories themselves were varied and interesting, and the tone of each shifted depending on the storyteller at the time always with some subtext relating back to what was happening in the main story. The rough yet composed art gave the horror a very gripping and macabre feel, but also added a lot of tenderness and life to other moments of the story as well (great example being the colorized pg. 14 of this chapter). I felt no sympathy for the fates suffered by Yuuma's Dad and Stepmom but do for the first police officer and Kido. In the end, they all became victims of what is now only the first ghost story in Hina's own Round of 100.
My "favorite" stories were Ch. 29 & 35, worth rereading for the horror and emotion respectively.
Thanks so much for the TL of this series.