[01: A party?]
[Nightingale_Chirping: Yes, it's a get-together for everyone to get to know each other and to change your Support partner if you meet the right person. It's considered a form of social activity. It doesn't matter if you don't know how to dance.]
[ 01: No, sorry, I'm not interested.]
[Nightingale_Chirping: Oh, alright... But your Support will be there.]
[01: Just let her be.]
It was normal to abandon an existing Supporter when they meet better ones.
During his last conversation with "GloriousMoon", he knew she was a mage and didn't really need his Elemental Spirit Blade. So, even though his Elemental Spirit Blade was an (S) grade, it wouldn't be something she would like to use.
The main reason she even agreed was probably due to his high Mana, which would be immensely useful to her. She would probably already look for someone else if it weren't for that.