It's apparently one of the worst clichés in the fandom's writing community. And I'm not saying it is a bad one just because it is — I mean, I agree, Daigo being a dark-ish character in fanfics seems reasonable.
But there are some points I'd like to bring up, because I found my fair share of terrible Daigo fanfics.
Just because Daigo takes the dark aesthetic doesn't mean he's going to be depressed all the time
Yeah, yeah, I get it, go ahead and play with the idea once! But I have seen multiple fanfics by one same person where they make Daigo a sad and dark character for ALL their stories. Like what the fuck??? Unless this is an AU or you are a tragedy writer, when writing for a Canon-esque fanfic, Daigo shouldn't be close to cutting himself or trying to commit suicide. Look at him in the show! He's normal!
THIS DOES NOT ONLY APPLY TO DAIGO!! Stop misrepresenting depression
Guys I cannot emphasize this enough. Depression and other mental illnesses aren't SUPPOSED TO MAKE YOU A FUCKING COOL KID. I see people going Hi I am a twelve year old and I am insane xoxo no i didnt get a doctor to check me out LOL and I see ghosts but no one else does I am better than you loser 😭😭✌️and LOLOLOL I straightened a painting does that mean I have OCD now 😝😝😝😝😝
No. Stop it. If you don't have a doctor to officially declare you are ill, then don't even bother. It's offensive towards the real people who ACTUALLY have the mental disorders.
And I've seen some people where they try to give Daigo a mental illness or depression in a story. I mean, I don't have a problem with it, but when they explicitly say so like "This is a story about Daigo having depression and all he does is try to kill himself." NO NO NO NO.
Depression is more than just Blah blah time to plan my suicide again! I cannot explain depression because it is complex and varies person to person. I actually know some affected friends and people (diagnosed by doctor), and they're offended by fakers and stories. They said having a mental disorder is so misrepresented by people on the internet, so it is hard for people to learn anything.
In short, don't bother making Daigo a victim of a mental disorder because He is sooo edgy and dark UwU and I think he seems cool with it! Unless you're actually trying to be serious with it, DO SOME FUCKING RESEARCH. Mental disorders aren't cool, whether you're trying to seem cool online or make an anime character cooler by giving them one.