Shadonia

Shadonia is the het ship between Shadow and Sonia from the Sonic the Hedgehog fandom.

Canon
Sonia appears exclusively in Sonic Underground and briefly in the Underground Zone in the Pre-Super Genesis Wave Archie comics. Shadow was introduced two years after the last episode of the TV series.

However, Sonia has made an unintentional cameo in Sonic & Sega All-Stars Racing, a game in which Shadow is playable. The creators stated that they mistook a fan art of Sonia for official art of Amy Rose.

Similarities

 * Both are technically one of the strongest characters in their appearances in media.
 * Both are able to attack using projectiles (Sonia can fire lasers from her keyboard, and Shadow can cast Chaos Spears).
 * They have met their counterparts of Knuckles the Echidna.

Fanon
This ship is fairly popular. It is among the most popular ships for Sonia, though it is not the most popular ship for Shadow. A group with this ship in mind was set up in November 2011. Two fan-fiction series are currently under its Literature category.

Three notable DeviantArtists are ShadowHRO, Shadonialuver and SirinaTheHedgehog, who have been making Shadonia fan art since 2019. ShadowHRO also archived a fan fiction by The Lord of Nothing featuring both characters. Some fan art of the ship despite Shadow as Sonia's knight in shining armour, do to her being a princess and the fact that Shadow's Camelot alternate reality doppelgänger is the Arthurian knight, Sir Lancelot. Along with them editing Sonic X screenshots of Sonic and Amy to feature Shadow and Sonia together in the said anime universe, or have the two riding motorcycles together.

Because Shadow is depicted as Sonic's rival and with Sonia being the later's sister in the Underground Zone universe, some have the blue hedgehog not being too happy about their relationship.

Fandom
DEVIANTART