Well, you could do a crossover where the Danganronpa students are transported to the RWBY world. They'd have to adapt to the Grimm and the Huntsman - Huntress system. Or perhaps create a scenario where the two universes are merged, and there are new rules for survival. The characters from both series would have to form alliances based on their skills and personalities.
One idea could be creating an OC who is a master of disguise. They could use this skill to gather information and try to outwit the mastermind. Another idea is an OC with a unique phobia that adds an interesting twist to the killing game scenario. For example, an OC who is terrified of the dark and has to face challenges in a pitch - black area.
How about a Danganronpa and Kingdom Hearts crossover? The Heartless could be used as a threat in the Killing Game, and the characters could travel between different worlds from Kingdom Hearts while trying to solve the mystery. Or a Danganronpa and Naruto crossover. Shinobi skills would change the dynamics of the Killing Game. Characters could use ninjutsu to either kill or protect, and the hidden villages could be the settings for the game.
One idea could be a crossover where the Total Drama characters are put into the Danganronpa killing game situation. For example, the challenges in Total Drama could be incorporated into the trials in Danganronpa. Another idea is to have the personalities of the Danganronpa characters influence the Total Drama competitions. Maybe some of the more devious Danganronpa characters could come up with sneaky strategies in the Total Drama challenges.
One popular idea is alternate universes. For example, a fanfic might explore what would happen if the characters were in a modern-day high school without the killing game. Another idea is character backstories. Fans often like to expand on the characters' pasts that were not fully explored in the original game. And relationship fics are also common, like exploring the friendship or potential romantic relationships between different characters.
One idea could be a fanfic that explores the backstories of minor characters in RWBY more deeply. For example, you could focus on a character like Velvet and create a story about her training before coming to Beacon. Another could be a crossover within the RWBY universe itself, like a team-up between different schools' teams that we haven't seen much of in the official series.
You could write a fan fiction where the characters from different Danganronpa games interact. Imagine Makoto Naegi from the first game meeting Hajime Hinata from the second game in a non - killing game scenario. They could exchange their experiences and learn from each other. Also, a fan fiction about a character's redemption arc would be interesting. Like if a character who has done bad things in the original game tries to make up for it in a new situation.
You could do a crossover with the Final Fantasy series. Picture the Danganronpa characters in a world filled with magic, summons, and complex job classes. They might have to complete quests or battles to progress, and the killing game aspect could be intertwined with the battles against powerful Final Fantasy monsters. For example, the murderer could gain power-ups from defeating certain bosses.
One idea could be to explore an alternate origin for the characters. For example, what if Ruby's silver eyes were a result of a prototype experiment gone wrong? Another could be to set the fanfic in a parallel universe where the Grimm are actually created by a mad scientist using prototype technology. And perhaps a story where the characters have to use prototype weapons that have unpredictable powers.
One idea could be exploring new stand abilities inspired by RWBY characters' weapons or semblances. For example, a stand based on Ruby's Crescent Rose could have the ability to manipulate time briefly like Ruby can move at high speeds. Another idea is to create crossovers within the RWBY universe using stands, such as having a stand user from a different part of Remnant interact with the main RWBY team and their battles.
For a 'rwby breeding fanfic', you might look at the idea of cross - species breeding if there are non - human characters in RWBY. Maybe a Faunus character breeds with a human - like character. This could bring up all sorts of interesting cultural and physical differences in the offspring. The fanfic could explore how the society in RWBY reacts to such cross - breeding, whether there is acceptance or discrimination, and how the characters themselves deal with the consequences of their actions.