The fanfic tells the tale of Robotnik's grandfather, Doctor Gerald Robotnik. It chronicles how he became the man he was. As a result, most of the major Sonic characters aren't in the fanfic and Shadow isn't even born until halfway in. Descent into Darkness doesn't take much influence from adaptations and instead opts to create and expand upon what is depicted in the mainline games.
Descent into Darkness is the first in a series of interconnected fanfics loosely based on the games. The series thus far consists of: Descent into Darkness, Ascent into Light, Lost and Found, Three There Are, In Memoriam, The Soul of a Weapon, and Dreamchaser. In Memoriam is a short fic where Shadow builds memorials for the ARK massacre victims.
These fanfics provide examples of:
- Birth/Death Juxtaposition: Maria was born a few days after her grandmother Mary was killed.
- Fantastic Racism: In Gerald's day, there was a tension between humans and dokan. Humans generally lived up north while dokan lived in southern countries. The two species were on peaceful terms, but they tended not to interact with one another. It's mentioned that some countries don't like dokan, but most of them just deport them instead of kill them nowadays.
- Fantastic Slurs: Funny Animals call themselves "byodokan", or "dokan" for short note . The politically correct term amongst humans is "furries", but more speciesist people call them "freaks" or "animals".
- Fictional Disability: NIDS is given more detail than in canon. It's an incurable autoimmune disease related to the nerves. If the person doesn't die of infection first, then they'll end up paralyzed and die from that.
- Fictional Earth: Sonic's world is named "Earth" but it's very different from our planet. For one, it has different continents. There's also the sentient, bipedal animals that coexist with humans.
- Interspecies Adoption: Shadow and Maria are referred to as siblings.
- Interspecies Romance: Subverted. Gerald finds himself attracted to a fox, but she already has a husband.