these aren't normal costumes. you'll know if you've read through the comics. anyways there is no visual depiction of two males having any kind of sexual interaction, so i'm not going to put the gay tag either. if you think otherwise, you can talk with a moderator or just use the report button.
I read the comic, the mc definitely identifies as male, and so does henry. They only embody characters within the suit, they explicitly mention roleplay multiple times. The boss even mentions that they were going to cum inside their suit, indicating that the costume is only an external change. The MC also says, and obviously believes, he had sex with henry, while talking to him in his male form. The gay tag isn't a gay sex tag, if two men are romantic or sexual with one another the gay tag is appropriate.
Technically it isn't even vaginal sex as it's a costume, not an actual vagina. If it were an actual vagina then you should probs add a rape tag as consenting to have sex with someone who lies about their identity and gender is extremely sketchy. The MC never agreed to have with Henry, he agreed to have sex with a girl who he believed was roleplaying a female student. Roleplaying requires informed consent of what you're getting into and safewords so that consent can be withdrawn. I mean, if as indicated
then there are even more issues regarding consent.
I can understand the transformation tag, even though it technically isn't appropriate as it doesn't alter your mental or physical state in any way, it just covers them, which is just an elaborate costume. But it defs needs a gay tag, the futa tag is probs fine, and it should probably have a rape tag given the numerous violations of both henry and the mc's consent.