This.
Because it looks cooler splitting open.I don't get the scabbard gimmick. Teacher can use his telekinesis to self deploy regardless of whether the scabbard splits open.
I like Fran's noble goals of wanting to get strong herself instead of only relying on Teacher. It's consistent with her ultimate goal of being the first black cat to evolve.
I was surprised by the depth of the lore they wedged in during episode 4. Very Delicious in Dungeon for their pantheon.