Some people think that shonen anime is for kids. This isn't true. While some of it is geared towards middle schoolers, some of it is actually targeted at older teens. That huge demographic range means that while some shonen is family-friendly, some of it deals with some truly dark content.
One of the darkest shonen anime is The Promised Neverland, which follows a group of orphans as they try to escape from a grisly fate - being sold as food to human-eating demons. There's also D.Gray-man, which features the souls of the deceased being used as high-tech weapons. If you love disturbing shonen, this list has something on it for you.