The Three Musketeers is the collective team name for Caleb "Crash" Waterfront, Katherine "Kathy" Argall, and Carmen Calandra. It was tangentally coined by Crash during Athalia Academy Season Two, after the trio defeated an army of fabric dummies commanded by Yutaka Ito.
The exact transcription of the nickname's origin is as follows:
Crash: "I personally can't take anymore hits today, did you two fancy heading over to another dojo or are you going back to sparring?"
Carmen: "I'd be happy going anywhere[...] The three of us might as well stick together, right?"
Kathy: "I'm good to go to another dojo as well." [...] "I was thinking of going to firearms practice next. Come with me please?"
Crash: "I'm feeling Musketeers stick together, so count me in."
Kathy: "The Three Musketeers? I like the sound of that."