Just say its a characters shirt from this webcomic

I would explain webcomics to your mother: regular comics but online for free from creative people who may otherwise not have had a chance to publish and share their work! Homestruck just being a comic that happens to be online! Your mother seems to be worried about who it's gendered towards which is easy enough to explain (it's for everyone!). These things are just new to her and when she was your age it was the same thing with her parents to a degree, though now adays innovation is really taking off so it seems like a huge jump in terms of ideas, values and interests that are new that younger generations are typically open to. If she still doesn't want you to get the shirt it's because she doesn't understand which makes her concerned, she just cares. Best of luck!

@Gryph
Yes, but my mother is a woman of many questions n she'll be like WATS A WEBCOMIC IS IS SUITABLE WILL IT GET A VIRUS ON UR COMPUTER

@Psy-mom
Thank you are you like a therapist or something you're amazing <3

Thank you! I really hope it helps you explain things to her and helps you see where she's coming from. :)
I'm no thera.pist, just some experience under my belt that comes with time.

((My momis only 51 and she is a homestuck fan))

((And my six year old niece. Along with my sisters))

^ dafuq omg

Thats why i can't get anything homestuck re-lated. :(