It’s probably most famously the name of the lead heroine in the Sailor Moon anime and manga, hence it’s a girl’s name, and on the hurricane/typhoon name list.
I have no idea how many Japanese girls are actually named Usagi.
Maybe an anime fan had input to the name list, and we can expect Typhoon Madoka some time.
Even if you don’t want deign to give Trump himself credit, he’s got very smart lieutenants working for him, like that Susie Wiles who co-managed his by-all-accounts “disciplined” campaign and was named Chief Of Staff a couple of days ago.