Otasune

"Life's more than a game of win or lose, didn't you say, Otacon? Now I understand. Trying to compare yourself with someone else, competing for a victory like squawking myna birds is foolish. But in your inner struggle, victory and defeat do exist. And right now, I'm losing. I'm yielding to the terror that comes flooding from within. I don't believe in God, Otacon, so you're the only one to whom I can pray. Give me strength to do this now. Give me the resolve to protect the paths you and Sunny will take through life, and the world Meryl and the rest will build."

- Snake, pleading for Otacon to help him stay alive however he can in the MGS4 Novel

Otasune is the slash ship between Otacon and Solid Snake from the Metal Gear fandom.

Main Metal Gear Series
Snake and Otacon are shown to have a close relationship following "Metal Gear Solid" (1998), which continues all the way into "Metal Gear Solid 4: Guns of the Patriots" (2008), which takes place nine years after MGS1. A few times in canon and in crossovers, they are referred to as "partners", but this is most likely intended to mean in business rather than anything else.

When Snake meets Otacon in his lab during the 2005 Shadow Moses Incident, he is initially hostile toward him due to thinking he intentionally designed Metal Gear REX with a nuclear arsenal. After explaining that wasn't his doing, Snake switches to being rather concerned about Otacon's wellbeing especially after he had witnessed two mysterious deaths (later revealed to have been caused by FOXDIE, a virus secretly injected into Snake) prior. In the MGS1 remake, "Metal Gear Solid: The Twin Snakes" (2004), Snake grabs Otacon's shoulders in the latter's point of view. Throughout the rest of the game, Snake keeps in contact with Otacon through the codec system, but they do not appear on screen together much again until the end of the game, if the player chose the "Otacon Ending". In it, the pair discusses where they'll go and what the future might hold for both of them.

Two years later, in "Metal Gear Solid 2: Sons of Liberty" (2001), Otacon and Snake are shown to be close friends who have started working and living together, as well as created Philanthropy, an anti-Metal Gear organization. Otacon has taken up being Snake's sneaking suit designer as well. Otacon seems to have become more comfortable with making snarky remarks and joking around with Snake, as evidenced by several lines in the Tanker Incident portion of the game. Snake was sent aboard the USS Discovery to prove the existence of a new Metal Gear prototype, while keeping a low profile since he and Otacon are on the run because of their anti-Metal Gear activities. After the overall failure of the mission, Snake fakes his death with help from Otacon.

In 2014, they continue to work and stay together on the Nomad, a helicopter which has enough room for them to live in. Their relationship has become a bit complicated, though, due to Snake's rapid aging caused by having been injected with FOXDIE. Snake wants to isolate himself to avoid a large outbreak of the virus, while Otacon is beyond worried for his health at all times. They are often close to one another in cutscenes, a lot of times of which are Otacon rushing over to make sure Snake's coughing does not impact him too badly.

Metal Gear Solid: Guns of the Patriots (MGS4 Novel Adaptation)
The MGS4 novel by Project Itoh, and localized by Viz Media, details information not given in the game itself. It is written in the point of view of Otacon, and follows the same story as MGS4, only focused on what Otacon is seeing and hearing from Snake, whom he says changed his life. Interestingly, the novel is the only source that states a death year for Snake, that being 2015.

Super Smash Bros.
In Super Smash Bros. Brawl and Super Smash Bros. Ultimate, the codec easter eggs on the Shadow Moses Island stage have Snake and a few characters from MGS1, including Otacon, discuss fighters' abilities and series of origin. In a lot of the calls with Otacon, they mess with each other, for example in Link's, Otacon calls Snake "Mr. Utility Belt" when he comments on how Link shouldn't carry around so much equipment in battle.

Metal Gear Solid

 * Snake is very touchy-feely with Otacon even right after they've met. Between lifting him up a foot into the air and grabbing one or both of his shoulders multiple times, it's safe to say Snake is very physically expressive.
 * In the "Otacon Ending", after Snake defeats his twin brother Liquid Snake, Otacon comes and uplifts Snake at the sight of Meryl's dead body. He tells him death isn't defeat and that life isn't all about loss while resting his hand on one of his shoulders.
 * Funnily enough, the "Otacon Ending" snowmobile cutscene is nearly identical to the one in the "Meryl Ending", specifically the music, setting, and many parallels in dialogue.

Metal Gear Solid 2: Sons of Liberty

 * During the Tanker part of the game, Snake goes along with what Otacon says except for the proverbs he recites, which he is still gentle in pointing out the mistakes in interpretation.
 * In the first area inside the Tanker, there are a number of lockers with posters hung up inside them, some of which are women only wearing bras and underwear... Going into first-person view and calling Otacon will trigger a codec call which results in the trophy "Snake Beater." The description states that Snake is caught by Otacon, but it's specifically the other way around; the player has to call Otacon in order to hear the call (strangely, Otacon does not sound shocked at what he's seeing, only hitting him with a "What do you think you're doing, Snake?" and "Try to remember the mission, if you can.").
 * The main goal of the Tanker is taking photos of the Metal Gear RAY prototype as Otacon asks, but if the player takes a photo of a poster with a shirtless man's chest and sends it to Otacon, he will say "...so, ah, this explains a lot. Not that there's anything wrong with keeping it to yourself, I mean, you know, it's your life and everything..." He will also say this if the player takes a photo of the Vulcan Raven action figure present in one of the rooms.
 * When Snake gets to the holds where the Marines are receiving a speech about Metal Gear RAY and its development, he can take pictures of the Commandant and send them to Otacon. The Commandant can appear without pants, and if the player takes a photo of that, Otacon's dialogue will be what it always is when he receives a picture he thinks is funny, but the player also unlocks the "Sexting" trophy.
 * After Otacon's stepsister E.E./Emma dies, he and Snake perform their own handshake, which is a representation of the Konami Code, and end it with an embrace. Right before it, Snake appears unusually serene as his expression softens into more comforting and welcoming than his near-permanent concerned look.
 * In "Snake Tales", a collection of non-canon extra missions presented in Snake's point of view in MGS2: Substance, there's one that deals with different universes and timelines, and part of it highlights how well Snake and Otacon know each other, and that Snake knew the person in front of him was Otacon, no matter if he was from his universe or not, and that they were friends above all else.

Metal Gear Solid 4: Guns of the Patriots

 * Snake and Otacon tend to touch each other a lot in this game, whether it be a grab on the shoulder or arm or, detailed in the novelization, Otacon rubbing Snake's back until he stops coughing.
 * The post-credits dialogue seems to follow the "in sickness and in health, until death do us part" format, with Otacon promising to stay with Snake until he dies and witnessing his last living moments. This then opens up into the MGS4 Novel, where Otacon introduces the reader to Snake and goes into extra detail about the events of MGS4.
 * There are a lot of allusions to Beauty and the Beast in the game: the major enemy organization, roses, Snake is often called a [man-made] beast, and FOXDIE is comparable to the spell the Beast is under. This would make Otacon the beauty, since both of the women Snake flirted with in MGS1 were unavailable by MGS4, another died, and the Beauty and the Beast Unit try to kill Snake.
 * Before Snake's final mission, Otacon offers to light Snake's cigarette even after being so opposed to him smoking, especially on the Nomad. This gesture was often seen as a signal of interest among gay men.
 * In the novelization, Otacon says he knows Snake best. It's unclear if he meant he knows the most about Snake, more than anyone he'd met, or if Snake was the person Otacon knew best in his life. Either way, what he says is true as in MGS1 Snake says that he isn't interested in anyone else, and that other people just complicate his life.
 * Also in the novelization, Otacon mentions that he and Snake would always take a walk together before a mission, explaining that they didn't care where as long as the sky was above them.

Children
In MGS4, Snake and Otacon have started taking care of a little girl named Sunny, whom Raiden rescued from the Patriots some time shortly after the events of MGS2 when she was a baby. She cooks sunny side up eggs, saying if they turn out properly cooked, Snake's mission will go well. and vice-versa for if they are cooked poorly. She is also very worried about Snake's health, as she frequently tells him about her dislike of his smoking habits and how much she wants him to quit. Both Snake and Otacon care about her like a parent would, but it's not until Metal Gear Solid Rising: Revengeance (2013), taking place four years after MGS4, that she is adopted. Snake seems to not be around, though it's unclear if he has passed away or if he simply does not appear.

Quotes
"Raiden, let me introduce you to my partner -- Otacon."

- Snake (disguised as Iroquois Pliskin) telling Raiden about Otacon shortly before getting attacked by Solidus Snake in Metal Gear Solid 2: Sons of Liberty

"Let me tell you a story about the Snake I know best. The Snake who was my friend. The Snake who changed my life."

- Otacon first introduces the reader to Snake and his complicated family, all of which mentioned use(d) the code name "Snake" in the MGS4 Novel.

Behind the Scenes
Creator of the Metal Gear series Hideo Kojima once compared the characters to Johnlock in a tweet on his Japanese-only account. Translated, it reads, "'SHERLOCK' has moved to the present day. The relationship between Sherlock and Watson in this drama is depicted with a sense of distance (looks like BL) that goes one step further than the traditional buddy's "buddy". Like Solid and Otacon in MGS. Each other is the only partner. So why not marry Watson?"

During an interview, Solid Snake's voice actor David Hayter expressed how much he likes working with Otacon's voice actor Christopher Randolph, saying, "...and to work with Otacon, that's my favorite. You know, we really- and that's where a lot of the joking comes in, 'cause Otacon's like, Snake's gay sidekick, you know? In a platonic way, everybody relax! But the point is, it's a lot of fun 'cause Otacon- you know, 'cause Otacon's so nerdy, and Snake's so tough that you get a lot of great, sort of, banter between them."

Additionally, Hayter and Randolph have stated they played a lot of Snake and Otacon's scenes as romantic. They also take fan requests on Cameo to voice lines based on the characters' relationship.

In 2022, there was a Twitter Poll for the Most Iconic Yaoi (MLM) Ships, in which Snotacon was a participant in. During the quarter finals, David Hayter commented with his support of the ship, also tagging Cristopher Randolph in his tweet. He did the same during the semi-finals, this time explicitly stating that he was rooting for Snotacon.

Fanon
Otasune is one of the most popular MGS ships, and lots of people, many of whom are not familiar with the series, have believed they are canonically and explicitly in a relationship. They are often physically affectionate on screen and talk to and about each other as if they are more than friends. The MGS4 novel is a source for a large amount of evidence, as Otacon talks about Snake almost like someone would about their significant other.

On the other hand, a number of fans dislike Snake and Otacon's relationship being interpreted as romantic. one reason being that they believe one or both of them are not attracted to or have feelings for the other. This was a popular argument topic years ago on sites like GameFAQs, which was the birthplace of the popular joke phrase, "Are Snake and Otacon.......you know...."

They take up a large part of each respective character's Tumblr tags, and are about 1/6 of all non-crossover MGS works on AO3.

The ship name "Snotacon" goes back to at least 2007, when it appears to have been in early use in MGS slash LiveJournal groups.

Fandom
FAN FICTION
 * Otacon/Solid Snake tag on FanFiction.Net

TUMBLR

Trivia

 * Shortly after meeting him, Otacon tells Snake to call him "Otacon", short for "Otaku Convention", during their Codec conversations instead of his real name (Hal Emmerich) or simply "Doctor", further elaborating that "an otaku is a guy like [him] who likes Japanimation." Even years later in MGS4, after he states he is no longer as interested in anime as he used to be, Otacon still uses that nickname.
 * As evidenced by the MGS2 script, Otacon was originally going to accidentally call Snake his real name ("Dave- no, Snake") during a mission. This confirms, if not already presumed because of how many years they spent together, that Otacon is one of very few characters in the series that knows Snake's real name (the MGS1 "Otacon Ending" is not 100% canon since Meryl dies in it, as she would seemingly and inexplicably appear in MGS4).
 * Since Otacon begins designing Snake's sneaking suits after MGS1, it means he was the cause of Snake's butt becoming such a meme and the major outcry from Snake's character model in Super Smash Bros. Ultimate where he appears to have been "censored" or "nerfed", as both Smash games Snake is in use his MGS2 design.