Is watching anime images, but not the series or any inappropriate moves they do, sinful and haram?
Is it haram even if you think it wouldn't lead you to any haram things or to watching inappropriate images of real persons?
My personal opinion, If you know the show is about lewd and edgy then yes, like high school DxD or other highly nude anime. But shows like naruto and other who have some episodes with nudes in them (usually blurry or covered) are is no way haram.
Read what the show is about is there are tags like, lewd or naked try to avoid them if you can.
Anything which leads you to watch some inappropriate images or videos or may bring you to do inappropriate move, is a sin and also affect your life circumstances badly.