Both series are set in a future where the world has become uninhabitable except for a few select places. Privileged people live within a walled city where they are ignorant to the lives of others living in the slums outside. In No.6, Shion is one of the privileged living in the wall. In Mother Keeper, Ricalna is one of the rebels living in the slums outside. In both series the protagonist ends up on the other side of the wall and learns that life there isn't what they expected and that everything they have thought to be true might be a lie.
Like No. 6, Golden Days has a love story between two boys that is not the focus of the plot. The plots of both are suspenseful, though they are in different genres. Both romances are more emotional rather than physical. They also both have female characters who play important roles.
Although the plot is completely different, the relationship between two male characters was extremely similar. I got the same vibe from Nabari no Ou as No.6 while I was reading it. Both manga have unique characters and refreshing stories.
Both manga are dystopic stories centered around pretty boys. Both series center around the relationship of two male characters in this setting, though in Inferno that relationship seems much less romantic. The atmosphere is the same.
Two young men fight against a corrupt organization. One is ruthless and intelligent, the other is forgiving and kind. There is a lot of guns and action mixed with scenes of character bonding. Both have a large cast of characters.
Though the stories in themselves aren't really similar, the main characters cross over nicely.
Allen Walker is like Shion with the scar on the same side of his face, brown hair which turned white after a near death experience, and his happy, innocent demeanor despite what he's been though.
Kanda Yu is similar to Nezumi with his bluish-black hair always worn in a ponytail (though longer), his irritation at how naive the main character is, his exceptional ability to fight, and his unknown origins.
Nezumi and Shion are like Fon and Jaques in certain ways. Fon and Nezumi both lost their families tragically. All the characters have learned that there are still people willing to help other people even at the detriment of themselves. There's also the theme of geniuses in both series, and the idea of a place that may seem ideal on the outside but is really corrupt underneath. Both have the main characters changing each other in many ways, and almost the same level of BL and darker themes.
- They both start off in a closed off place/region where everything is being controlled and is considered "perfect".
- The main characters both know that where they live is a false utpoia
- They run into a wanted criminal and end up saving them and by doing this it changes their lives forever...
Both these mangas are quite different; no.6 is a dark story about a false utopia, Seven Days is a Love story. Both are good in their own ways. What they have in common is how they portray queer characters; with respect and without fetishizing them; good writing in this part.