I was a tad confused concept wise (but this is because I haven't seen Letter Bee), but it was a very touching piece emotionally. Definitely peaked my curiosity in the series.
The ending was very abrupt, which was saddening to a small degree.
I wasn't font of the sudden music change at 2:35. I think it could have been cute/implemented better, ESPECIALLY since it was the end credits, but I thought for a few moments that it was continuing.
Still, I enjoyed it. Glad to see something unique!