If I understand it correctly (it’s not impossible I don’t), the illustration is more or less their branding/logo/mascot. It’s basically a non-intrusive advert for Anubis that helps to spread awareness of something like that existing. It also doubles as a status indicator.
And I don’t see any issue with it, since Cloudflare for example also slaps their logo and text “Performance & security by Cloudflare” on their “Checking if the site connection is secure” page. (Yes, it’s smaller, but still.) Non-intrusive promoting of themselves, especially when giving the project for free, is imo acceptable.
And it also really doesn’t matter. Vast majority of site visitors won’t condemn the whole project for being unprofessional just because its website uses a scraper protection that has anime girl as a mascot.