I dont understand the ending ?

Are 당신 talking about the very last ep? When Tomoya is telling the two girls his life story? Fuuko didn't find Ushio in the woods, they were having a play date. Even though Fuuko is supposed to be a high schooler, she's a bit of a kid, so her main friend is Ushio.

Do 당신 mean when it shows Ushio at her old age and then at her young age? I think it's just there to show the connection that the girl in the other world is in fact an older version of Ushio. I am pretty sure Fuuko only saw Ushio as a little girl and didn't actually see her as her older self.