Who does the commander canonically oath?

I realize this is probably a loaded question, so I'll try to be a bit more specific. I haven't read the manga, so I'm not sure which T-Doll the commander canonically oaths, assuming (A) They choose any at all and (B) the commander isn't Gentiane unless she's a lesbian.

Sex jokes aside, I really want to know. I would assume it would be M4, since naturally she is the main protagonist, but otherwise, I would assume that canonically the commander simply chooses to keep his/her relationship with his/her subordinates strictly professional.

Let me know what you think.