@HajimeteNHK I'm not sure, but I think he's talking about one of the Japanese yearly festivals centered around remembering your ancestors. At first I thought it might be Obon, but he says on the first page that "September is already over" and Obon is typically set earlier in the year. It could be a family memorial as well, a similar celebration of ancestors that is specific to his family, I suppose.
Of course, I could be completely wrong and he's actually talking about a memorial for a recently deceased relative. I guess we'll have to wait for next chapter to find out.
My interpretation of the last panel is that it's seen through Madoka's eyes. He's actually going away somewhere, and won't be passing by her window every day for a while. Maybe she'll miss him?
@Catsuey I keep saying it, she's a Yokai! (I'm actually hoping that the secret to how she's able to change her room and her outfit seemingly beyond the laws of nature will never be revealed to us readers. It might be more entertaining that way)