I have a problem. I'm trying to upgrade the arcane ring in the fuse machine, but when the game asks me to pick an item, I cannot for the life of me find the ring anywhere in the selection. I know I have it in my inventory because I have it equipped.
Try this:
1) make sure that Celica does not carry it on herself, that is, that it is only in the main inventory, and not in the one with 3 cells;
2) come into the lab the next day and try again.
In addition, some items have a limit on upgrades. The options available to you are displayed in Agranor's library, in the magic book of fusions.