Before Keith and Shiro became the Red and Black Paladins, they met at an undetermined point in the Galaxy Garrison, an institution for training astroexplorers. While exactly what transpired is unknown, Keith has frequently stated in the show that it deeply affected him, even saying in the premiere for Season 3, episode 1, that, "Shiro was the only one that didn't give up on me––I won't give up on him." Keith was expelled from the Garrison after Shiro went missing during a mission in space, presumed dead due to his own piloting error.
It has been confirmed in canon that Shiro is one of the most important people in Keith's life. In the Blade of Marmora, Keith's suit allowed him to hallucinate his greatest hopes and fears. In the first hallucination, Shiro appears as Keith's greatest hope, with the hallucination-induced Shiro subsequently abandoning him as his greatest fear.
Shiro and Keith have engaged in a lot of casual and comforting touches over the course of the four seasons, including, but not limited to: shoulder touches, clasped hands, and emotional hugs. This is exclusive to their dynamic, and they are not shown to exhibit this kind of bone-deep familiarity with any of the other characters on the show.
Likewise, they are very comfortable with each other, to the point where many fans of the ship have speculated about the exact nature of their relationship pre-Kerberos, and Keith is the only person Shiro allows himself to be truly vulnerable around.
Along with Klance, the ship has really taken off for modern audiences in the last couple years. This is thanks to Voltron: Legendary Defender Season 2, produced by Studio Mir (Legend of Korra). A lot of the writers and directors for Voltron migrated from Korra, famed for it's bisexual ending, and have made comments hinting at possible LGBT content, including the quote, "I think I'll just let that play out as we go. No comment on that question," when prompted about future LGBT content. Although the ship is not confirmed in canon, many fans still enjoy Keith and Shiro's dynamic in a fanon environment due to the deep connection Keith and Shiro have been shown to share over the last four seasons.
The ship has received hate because of its prospective age gap. Many contradicting age ranges have been mentioned by many different official sources, some fans consider that there are no definitive set ages for Keith or Shiro, or for any of the other Paladins, while others do not consider any published age information canon.
The ship has been acknowledged by countless members of Voltron's production team since the show first aired, further supporting it as a ship for fans to enjoy. These instances include:
- Members of the production team such as art director Chris Palmer, Steve Ahn, Christie Tseng, Barlee, and Lauren Montgomery liking Sheith fanart on various social media platforms.
- Voice Actors such as Bex Taylor-Klaus and Josh Keaton mentioning the ship on several occasions on social media, including when Keaton suggested the ship name "sheith", and the instance wherein Taylor-Klaus declared that Keith is a powerbottom in response to Keaton posting a picture of red and black shoes.
- Members on the staff such as former art director Chris Palmer and Kim Il Kwang produced art that emphasizes the bond between Shiro and Keith, and are often theorized to have romantic undertones.
- “At this moment, your friend desperately wants to see you.”
- —Kolivan, Blade of Marmora
- Keith – It's good to have you back.
- Shiro – It's good to be back.
- ―The Rise of Voltron
- “If it wasn’t for you, my life would have been a lot different.”
- —Keith, Across the Universe
- “Shiro is the only person who didn’t give up on me - I won't give up on him.”
- —Keith, Changing of the Guard
- Shiro – It's good to have you back.
- Keith – It's good to be back.
- ―The Ark of Taujeer
- Shiro – How many times are you gonna have to save me before this is over?
- Keith – As many times as it takes.
- ―Taking Flight
- “I love you.”
- —Keith to Shiro; The Black Paladins
- Keith pilots the Red Lion, which forms the right-hand of Voltron, thus making him the right-hand man of Shiro, who lost his right arm to the Galra.
- Keith is part Galra, and Shiro's right hand was replaced by a Galran prosthetic.
- The ship name was coined by Shiro's voice actor, Josh Keaton, after he proposed "Sheith" on his Tumblr blog.
- Shiro's Bayard, when combined with Keith's, activates Voltron's Blazing Sword, and it's a joke within the community that Shiro lights Keith's fire.
- In an AfterBuzzTV interview, it was brought up that the fans discovered Keith and Shiro in the background flashback with Matt and Pidge. Lauren and Joaquim congratulated the fans on a well done for finding the easter egg. Lauren commented with "I put that shit in there—Oh, I just said a bad word." and "Shiro was still his guiding light, it was good."
- It placed #2 on Tumblr's Fandometrics ship list on June 18, 2018. (3 days after Season 6 aired.) This is the highest the ship has been on the list.
- The Paladin's Handbook guidebook states that Shiro is 25 and Keith is 18, though there is some doubt as to whether this information is accurate to the canon because the book was not reviewed by executive staff. 
- The show staff previously gave "safety zone" ages of "25" and "late teens" respectively, while agreeing that Shiro is an adult and the other Paladins are not.
- Official show descriptions describe the Earth paladins as "five teenagers", placing Shiro as a teenager in contrast to his published age; Josh Keaton grants some insight into the discrepancy by stating that during production of the show as early as the voice actor auditions, the pitch was "five teenagers", but certain character models ended up looking different than the description, so the writing adapted to the finalized designs. This suggests the book does not take the ages from the original pitch as staff feared and reflects the organic changes they have made, while the official show description is the original pitch that is inaccurate to the canon.
- ↑ Josh Keaton's Tumblr
- ↑ The Fandometrics: Week Ending June 18th, 2018
- ↑ Den of Geek: Is the Paladin's Handbook Canon? August 2017
- ↑ San Diego Comic-Con 2016
- ↑ Let's Voltron: Shironanigans! With Josh Keaton - 00:43:00 "When we first started recording this, everything kind of changed. The early description of the show was like "five teenagers" or whatever, and that's the breakdown we got when we first started recording the show, when we first auditioned for it and everything it was that. And then over the course of the show things kind of change and certain models come back looking different than what the description was. So then the writing kind of - I wouldn't say changes but... adapts to the way the character looks now. And you know a lot of things change in the early production of the show."
|Ships||het||Allurance • Allurivan • Hallura • Hidge • Holtcest • Hunay • Kacxa • Kallura • Kidge • Lotacxa • Lotidge • Lotura • Mallura • Nymatt • Plance • Plaxance • Shallura • Shayance • Shidge • Zaggar|
|slash||Alforan • Hance • Hatt • Heith • Katt • Keitor • Klance • Koliveith • Lancelot • Latte • Lokon • Shance • Sharkon • Shatt • Sheith • Shendak • Shlav • Shotor • Shunk • Svance • Svav • Sveith • Uliro|
|femslash||Aczor • Nymallura • Pallura • Shayllura|
|poly||Hunayllura • Klunk • Plunk • Shaymallura • Sheitor • Shkatt • Shklance|
|family||Patt • Team Voltron Family|
|Characters||female||Acxa • Allura • Ezor • Haggar • Pidge • Krolia • Romelle • Shay • Zethrid|
|male||Coran • Hunk • Keith • Kolivan • Lance • Lotor • Matt • Sendak • Shiro • Slav • Sven • Zarkon|