終ノ空remake OST - Unknown Title

This song plays a few times in Tsui no Sora Remake and while it sounds completely new to me the placement in the files with the Subahibi songs (with the name bgm108 as opposed to TnS songs labeled called 201 and so on) suggests its from there, but I don’t remember it. While the metadata mentions Sakura no Uta, it doesn’t appear to be from there either. I would assume it was composed for TnS Remake but it’s much longer than any of the other (presumably) new songs so I’m uncertain. Tell me if you know where it’s from.