Shadow is a creature that was created to help make a cure for Maria's fatal illness. The two of them were raised alongside each other on board the Space Colony ARK, they formed a very close bond and were like siblings to each other. Maria is, is by far the one person that made Shadow the happiest, and they shared the same dream; to visit Earth.
Unfortunately, Maria was shot and killed by G.U.N, who deemed Project Shadow to be too big a threat to the world. They eliminated everything they could in relation to the project, including the people. Her last parting words were "Sayonara, Shadow the Hedgehog," Shadow still stays strong to keep his promise to her no matter what and mourned her death.
This backstory is roughly the same in all canons where Shadow appears, excluding Sonic Boom.
In some canons, Shadow has felt some kind of fondness for girls who remind him of Maria. Examples include Molly from Sonic X and Hope Kintobor from the Pre-Super Genesis Wave Archie Comics, the latter of whom was actually related to Maria. In addition, in Sonic Adventure 2, it was Amy's words reminding him of Maria that convinced him to save the world.
This ship is one of the most popular ships for Shadow along with Shadouge. A common fanfiction storyline for this pairing is a story were Maria is brought back to life as a hedgehog.
- shadaria tag on DeviantArt
- shadria tag on DeviantArt
- shadmaria tag on DeviantArt
- shadowxmaria tag on DeviantArt
- mariaXshadow-fanclub tag on DeviantArt
- The co-creator of Shadow and writer of Sonic Adventure 2, Shiro Maekawa, retweets Shadaria fanart on Twitter.