How you file a TOS violation report like this...

[SturmChurro]

Technically, impersonation falls under 3.4:

3.4 Impersonation. You may not impersonate any person or entity or fraudulently hold yourself out as a Square Enix employee, representative, or any other Square Enix-connected person or being affiliated with any such person or entity. This means you cannot log into someone else's account, or deceive or mislead other people as to your identity. For your own safety, we encourage users to safeguard their privacy, remain anonymous, and never give out personal information to other users.

It depends on how broadly SE or any particular GM wants to enforce this. However, relevant to this, as stated in prior posts, account sharing is also a violation:

3.1 Sharing Account Information. You may not share your account or login information (such as your Square Enix ID and password) with anyone except your legal guardian, your minor child, or Square Enix. You are responsible for maintaining the confidentiality of your account and login information, even from your friends and family. If you violate this provision, you may unexpectedly lose access to your account to a third party without recourse against Square Enix. Square Enix will not be obliged to credit your Square Enix Account with Crysta or other points or awards, which may have been used by a third party as a result of the violation of this clause.

https://support.na.square-enix.com/r...1&tag=users_en

In addition, this sort of behavior may also be interpreted as "Nuisance behaviour".

https://support.na.square-enix.com/f...la=1&kid=68216

Nuisance behaviour
"Nuisance behaviour" means speech or behaviour that hurts others or obstructs game play, but which is not classified as harassment. Even if it was not the intention, a penalty may be imposed if the end result was that another person was hurt or obstructed.

Below is a non-exhaustive list of examples of nuisance behaviour:

[...]

Impersonation
"Impersonation" means impersonating or fraudulently claiming to be other players, SQUARE ENIX employees, or any third parties. This could involve using a name that resembles the character name, Free Company name, etc. or is used by another person, or using a name that is the same as or similar to the name of a Square Enix staff member.