In the BSD manga, unfortunately, Dazai did die. His death was a crucial moment that influenced the direction of the story and the relationships among other characters.
One common theme is identity exploration. Since Dazai is a complex character, when he crosses over into different universes, he often has to re - evaluate who he is. Another theme is the clash of different worlds' values. For example, if he crosses into a more morally strict world, his rather ambiguous moral compass creates interesting conflicts.
One great 'bsd dazai crossover fanfiction' is 'Dazai in Another World'. It takes Dazai from BSD and places him in a fantasy setting. The story plays with his character traits in a new and interesting way, exploring how he'd interact with the new world's rules and characters.
Well, since it's related to Bungo Stray Dogs, perhaps it's about a special entrance exam within the agency or some other organization in the story. Dazai is a complex character, so it could involve his schemes or his interactions with other characters during this exam. It might also explore the rules and challenges of this exam, which could be unique to the world of BSD.
Another option is Tumblr. There are a lot of fans who post their Ash Lynx fanfic on their blogs. You can search for relevant tags like #AshLynxFanfic or #BananaFish (since Ash is from Banana Fish) to discover these stories. Some of these Tumblr fanfics are really creative and offer unique perspectives on the character.
One common theme is self - discovery. Since it's in the first person, the character of Ash Lynx often reflects on who he is and what his purpose is. Another theme is survival. Given his tough circumstances, many fanfics in the first person show his fight to stay alive.
The setting is important. If it stays true to the original world where Ash Lynx exists, it adds authenticity. It could be the gritty streets and the dangerous underworld he is part of. The description of these elements from his first - person perspective can really draw the reader in. Also, a good plot that involves his relationships, whether it's his friendships or the more complex romantic interests, is key. It should develop in a way that makes sense for his character and the overall story world.