Tbh not much different from their reactions to other cartoons. Tho my dad was a big Speed Racer fab way back in the day, which is an anime so yeah...
About the only thing they’ve ever said is “if the characters are Japanese then why do they look white?”
Overall they think most anime is strange but they just kinda leave me to my own when it comes to it. Tho I do make it a point to tell my mother if I’m watching something like Devilman Crybaby - I go “hey mama, you might hear some weird sounds from my TV but I promise it’s not porn”.
Oh, actually I just remembered, me and my dad did watch Attack on Titan together. He walked in while I was watching it and I was on episode 2, he got into it and he kinda wanted to see more. Tho he was convinced Armin was a girl no matter how often I tried to correct him (he’s hoh so yeah). But the main thing is we both like violent media. We’d already watched SPAWN (the animated one) together so lol.
At this point my parents chalk it all up to me liking weird stuff and they don’t try to understand it.