Keith met Romelle when he, Krolia and Cosmo came across the Altean colony, while searching for the unique kind of Quintessence, where Romelle told them what had happened to her brother, and many other Alteans, after the trio explained their mission to her. Even though it was the Galra, Krolia and a half of Keith's race, that destroyed Planet Altea and had forced many Alteans into hiding from the rest of the universe, Romelle chose to trust them. A choice that allowed her to uncover the truth and to be one of the first Alteans to leave the safety of the colony, so Keith could bring her to Castle of Lions and expose Lotor's crimes. When they got to the castle-ship, he let Romelle tell Coran and the rest of the Paladins her story, from how the colony came to be to Keith helping her to gain the answers to her long-asked questions.
After the Castle of Lions was destroyed to prevent the holes of Lotor's jumps from truing up the universe, along with the real Shiro's return, Romelle accompanies Keith and the others on their long journey back to Earth. In "The Journey Within", as their journey seems to be taking too long to reach Earth, they get hit by a void that motionless frozen the Paladin's passengers where Romelle is one of them, until the Paladins formed a stronger bond between them to which allowed their passengers to become unfrozen, before Voltron delivers all of them straight to Earth's solar system. Once they all arrived at the Galaxy Garrison on Earth, Keith, Romelle and the others were given orange Garrison uniforms to wear.
Shortly after Voltron saves Earth and were ready to free the rest of the universe, Romelle becomes a member of the Atlas crew so she could help Keith and the others in their task and to make sure that they stop Lotor's mother.
The stander reason as to why people have shipped Keith with Romelle could simply be due to Keith being one of the first outsiders she'd met, that aren't Lotor or his Galra doctor soldiers, and it being Keith who had helped Romelle expose Lotor for his crimes to the people that have helped her to prevent other Alteans being harmed by the Galra-Altean prince, like her brother. Since helping someone to get justices for their loved ones and showing them the rest of "world", have been one of the many first stepping stones that can lead to a romantic relationship.
Some fans like to see the ship an an interesting contrast that could be introduced if they were in a romantic relationship. Romelle is more bubbly, curious, and sometimes acts daring, while Keith is quieter and has a warrior demeanor to him, which is why some see their relationship being of an outgoing/shy or lone wolf romantic trope.
On AO3, the ship only has 25 fanfics. It also has a reasonable size fanbase on Tumblr.
|SHIPS||het||Allurance • Allurivan • Hallura • Hidge • Hunay • Hunelle • Jamonica • Kacxa • Kallura • Kidge • Komelle • Krolidad • Krolivan • Leiffin • Lotacxa • Lotura • Mallura • Nymatt • Plance • Romatt • Romance • Shallura • Shidge • Zaggar|
|slash||Adashi • Corance • Hance • Heith • Jaith • Katt • Keitor • Klance • Koliveith • Lancelot • Latte • Shance • Sharkon • Shatt • Sheith • Shendak • Shlav • Shoran • Shotor • Shunk • Svance • Svav • Sveith • Uliro|
|femslash||Acxlura • Kromelle • Pallura • Romura • Shayllura • Veracxa • Zezor|
|poly||Jeiro • Klunk • Pallurance • Sheitor • Shkatt • Shklance|
|CHARACTERS||m/f||Allura • Hunk • Keith • Lance • Lotor • Matt • Pidge • Shiro|