Tragic Bromance

This trope refers to a specific Plot, often seen in ancient epics. In it, two heroes are intensely close friends. Unfortunately, the one who's not the main character dies during the course of the story. The death has a profound effect on the remaining hero, and changes them forever.

It's important to note that 1.) The two cannot just be friends or acquaintances. They have to be REALLY close, and 2.) The supporting character's death needs to be a huge turning point in the story.

Anime & Manga

 * Tengen Toppa Gurren Lagann - Simon and Kamina
 * A little confusing since they consider each other brothers, despite not being blood related
 * Nabari no Ou - Miharu and Yoite.
 * This occurs twice in Neon Genesis Evangelion to Shinji, first with Toji and then with Kaworu.
 * Legend of Galactic Heroes: Reinhard and Kircheis. How much does this trope play out? Comparable to Gilgamesh&Enkidu or Alexander&Hephaestion.
 * There's also Reuenthal and Mittermeier, the "twin stars of the Empire."

Comic Books

 * DC Comics
 * Hitman - Tommy and Natt
 * Booster Gold and the Blue Beetle, though in some continuities, the new Beetle serves as Replacement Goldfish. Beetle's death makes Booster go from an egotistical, fame-seeking buffoon to wanting to genuinely be a heroic hero who contributes something.
 * Marvel Comics
 * Cap and Bucky.

Film

 * In Forrest Gump, Forrest and Bubba. After Bubba's death, Forrest fulfills his friend's lifelong dream by buying a shrimping boat.
 * Several John Woo films
 * A Better Tomorrow - Sung Tse Ho and Mark Gor
 * A Better Tomorrow II - Sung Tse Ho and Sung Tse Kit
 * Inverted in The Killer with Ah Jong and Inspector Li Ying
 * Hard Boiled - Tequila and Alan
 * Brian's Song - Brian Piccolo and Gayle Sayers (yes, he's male).
 * An epic womance: the two female scientists from Volcano. The remaining scientist (Anne Heche) is that much more determined to convince FEMA that there's really a volcano starting in Los Angeles because her best friend died to prove it.
 * In Captain America the First Avenger, this is the fate of James "Bucky" Barnes. This also follows the comics, though in the film Bucky and Steve are the same age, while in the comics Steve is older.
 * Happens due to KHAAAAAAAAAAAAAN! in Star Trek II the Wrath of Khan to Kirk, who has to watch as Spock dies. Of course, in the next movie Spock gets better, but at the time it was intended to stick.
 * A version of this happens in X Men First Class, in which Magneto and Professor X form a close friendship, but ultimately part because of a major difference in ideals. Notably, neither is killed, though Xavier does sustain a permanent injury that leads to Magneto cradling his cripple.

Live Action TV

 * Sam and Dean Winchester manage to do this to one another multiple times. Dean is the ruling champion, but if it weren't for Sam's first major death the whole plot from the beginning of season three onward would not exist in any recognizable form.
 * Getting him out of it caused Dean to die at the end of season three, which caused Sam to have a major character shift in the four months between then and when Dean got better again at the start of season four; and the combination of what the two of them did while Dean was dead set up the need for Sam to die at the end of season five...
 * Dean's 101 deaths during one season three episode hit Sam pretty hard, too, especially the one that last six months before the bastard undid it. And hence the title of reigning champion. Also the fact that he stayed dead the longest.
 * Sam may have been resurrected quickly after the season five finale, but his soul stayed in Hell for over a year.
 * And as of the end of Season 6, it looks as though Dean and Castiel are headed in this direction.
 * Although Buffy gets better after just a few months, Buffy and Willow between the season 5 finale and the season 6 premiere of Buffy the Vampire Slayer totally fits this trope. Buffy's death causes Willow to go into a spiral of desperation and bargaining that eventually leads her into extremely morally ambiguous territory in her effort to resurrect her best friend, leads to her sliding into Drunk With Power, and emotionally sets her up for a Despair Event Horizon after her unrelated romantic tragedy involving Tara one season later.
 * Shut Up Flower Boy Band has one of the members of the titular band die in a tragic fashion. Being teenagers, the rest of the band doesn't take his death too well.
 * John is devastated by Sherlock's in The Reichenbach Fall. He's not even aware that the reason Sherlock.
 * Horatio and Archie's friendship in the Horatio Hornblower TV movies is an arguable example, although the emotional fallout after Archie's Heroic Sacrifice and death isn't explored overtly in the subsequent series.

Literature

 * The Bible - David and Jonathan
 * The Iliad - Achilles and Patroclus
 * Landon Parke-Laine and Anton Next in the Thursday Next series. Especially tragic because Landon's testimony in the investigation of the events that killed Anton turned Anton's name to mud for all history.
 * Sherlock Holmes and Watson, when Holmes apparently dies in The Final Problem. Luckily, he was just hiding.
 * The Silmarillion - Turin and Beleg. Made even worse by the fact that Turin was the cause of Beleg's death!
 * Raistlin's ascension to the tower of high sorcery leaves Caramon a drunken wreck for years. Without his brother, he felt completely unneeded. It is only after Raistlin actually dies that he is able to move on with his life.

Mythology

 * Greek Mythology has Achilles and Patroclus. It's Patroclus' death that motivates Achilles to get out of his tent and kick some Trojan ass.
 * Norse Mythology has Örvar-Oddr and Hjalmar.
 * The oldest known legend in the world, The Epic of Gilgamesh, is one such tale. The whole story after the first act is about Gilgamesh's quest for immortality, to which he is driven by the death of his close friend and comrade Enkidu.

Theatre

 * Romeo and Juliet - Romeo and Mercutio.
 * West Side Story - Tony and Riff

Video Games

 * Final Fantasy VII - Cloud and Zack
 * Only touched upon in flashbacks during the game, but elaborated in other entries of the franchise such as Last Order, Crisis Core, and Advent Children.
 * Persona 3 - Shinjiro's death, from Akihiko's point of view. Bonus Points for the allusion to Castor and Pollux (see Mythology).
 * Solid Snake and Gray Fox in Metal Gear 2, but properly explored in Metal Gear Solid, where it's shown Fox's death has broken Snake's heart when Fox Comes Back Wrong as a cyborg desperate to fight Snake to the death so he can find some peace.

Real Life

 * Alexander the Great and Hephaestion, who actually compared themselves to Achilles and Patroclus on more than one occasion, even laying wreaths on their respective graves at Troy.