CLAMP created some characters that had an absolutely miserable backstory, some are so really tragic that Sumeragi Subaru’s backstory might seem not so terrible after all.
However the quote ‘At least you’re not Subaru’ is still very popular in the net and, so far, it hadn’t been replaced, as far as I know with any other ‘At least you’re not (insert another character’s name here) ’ yet.
Some people might legitimately wonder why. Why should Subaru be considered that ‘special’?
Well, everyone has his own reasons for not wanting to be Subaru, some can sound very reasonable while some others… less (sorry but I’ve an hard time believing Subaru’s worst tragedy is he’ll die as a virgin… -_-;;;).
1) Subaru is one of their main characters from one of their oldest series. ‘Tokyo Babylon’ in which he first starred started in 1990 and ended in 1993 with an ending that’s definitely sad. RG Veda, their first work, will end in 1996 so people will know of the tragic ending of many characters afterward.
2) Subaru is one of their most loved and popular characters with Seishiro/Subaru as one of their most popular pairing and people wanting an ending to ‘X’ just because they want to know what will be of Subaru or hating the X movie because it killed off Subaru rather soon, complaining that the X anime cut the scenes in which he was cool (the fight with Nataku), didn’t properly summarize his story and even changed his fate and waited like crazy for him to show up on Tsubasa, loving him as Tsubasa character when he has such a minor role it could be almost forgotten. The name ‘Subaru’ says immediately something to many CLAMP fans while they might be not so familiar with Kujaku or not so emotionally invested with Fai. The new CLAMP fans often end up reading all works at a short distance from when they’ve read the new works but old CLAMP fans might have stopped reading new CLAMP works.
3) It’s a habit, really. People started to say so and even if it was discussed if someone should replace him in the end we’re used to say so. It’s a meme, a famous quote. It’s hard to stop just because.
4) Subaru is still alive but apparently in the manga has no hope of being happy. Characters who died a tragic dead like Su from Clover or Emeraude from Rayearth seem to have found peace in death and, at least, were loved before dying. They often die of their own choice, giving their life for a cause in which they believe, like again Emeraude or her beloved Zagato, or clone Sakura from TRC, or Kujaku from RG Veda (or many other characters from RG Veda as that manga has plenty of people dying) or at least get to see their last wish fulfilled like Nataku from X and Su from Clover.
The ones that instead don’t die but had a tragic past are always shown as free to move toward a happy future circled by their friends, like Fai from Tsubasa but also like Ashura and Yasha in RG Veda (who’ll be together), like Ran from Clover who’s living with Gingetsu whom he cares deeply. This gives out the idea even though they had a horrible time in their past in the end everything went well. People are also sure that everything will end well for Kamui, even though his story is really similar to Subaru so… although he’s frozen in time, his fate isn’t seen as hopeless.
All this didn’t apply to Subaru. Forced to live in order to keep alive the last piece of Seishiro he feels more or less like an empty shell. He doesn’t have a wish and, as people make wishes in hope to gain happiness, this can take only as either Subaru is already happy and has nothing more to wish for or there’s no way for Subaru to be happy according to him so he doesn’t even have something to wish for. Regardless from Fuma/CLAMP declaring that Subaru was happy, Subaru’s face seemed to express everything but that. In the manga he’s not moving toward the future, possibly circled by his friends like he’s doing in the anime. Many think it would be an act of mercy to put him out of his misery.
Subaru is viewed as someone seriously depressed, who’d like to die and yet can’t and must continue drag his existence on alone, doing Seishiro’s job for which I fear he’s even less suited than his own, without hoping for any chance of being happy all the while still caring for others enough to try and give tips to Kamui. So it’s not a matter of the amount of misfortune, it’s more a matter of the result. Subaru came out from his misfortune as completely crushed without even managing to save the only person in the world he loved more than the world itself or to be mercifully killed. Sure, there’s still hope even for him as X is unfinished but while many are willing to bet Kamui might have a chance, no one is betting on Subaru. And that’s why, in the eyes of many, make Subaru the saddest character. We can’t even hope things will go better for him without him going OC or without wishing for him to be finally allowed to die.
That’s why no one wants to be Subaru; because although he’s alive, for many, him included, there’s no hope for him to be happy.