One common trope is the survival aspect. Just like in the original 'Highschool of the Dead', in fanfics, the gamer characters often have to use their gaming skills to survive in a zombie - infested world. For example, they might use their knowledge of strategic games to plan escapes or fortify their hiding places.
The 'alternate self' trope is popular. The gamer might meet different versions of themselves in various multiverses. Then there's the 'cosmic battle' trope. They get involved in huge battles that span across universes. Also, the 'mystical guide' trope is often seen. A mysterious figure appears to guide the gamer through the complex multiverse.
Rias is also a common and popular choice. Her beauty and leadership among the devils can be explored in relation to the gamer aspect. For example, she might be involved in a strategy game within the fanfic where her leadership skills are put to the test, or she could be a love interest for the gamer protagonist.
One popular trope is the 'enemies - to - lovers' aspect. Since Draco and Harry were enemies in the original series, seeing them cuddle after going through a journey of changing their relationship is really appealing. Another is the 'hurt/comfort' trope. Maybe one of them is injured or emotionally distraught, and the cuddling is a form of comfort.
One popular trope is the 'Training Bond' trope. Since they often train together in the original series, in yuri fanfics, this can be a starting point for deeper emotional connections. Another is the 'Protect Each Other' trope. For example, Kale might be in a dangerous situation and Caulifla would go to extreme lengths to save her, which then leads to a realization of deeper feelings. And the 'Shared Power' trope can also be common. When they combine their powers, it can be a moment of intense closeness and a catalyst for romantic feelings in fanfics.
The 'hurt/comfort' trope is quite common too. Maybe Cal gets injured during a battle, and Merrin has to take care of him, which deepens their relationship. Also, the 'soulmate' trope can be found in some fanfics, suggesting that they are meant to be together on a deeper, almost spiritual level, which ties in well with the Star Wars universe's themes of destiny and the Force.
They often use game - like interfaces. For instance, a character might see a virtual HUD (Heads - Up Display) that shows their health, ammo, or the number of zombies nearby. This gives a very gamer - centric feel to the story.
Survival is a very popular theme. Fans like to write about how the characters find food, shelter, and weapons in the zombie - infested world. Another is the exploration of the characters' relationships in a non - romantic way, like how they build trust and teamwork.
One of the popular tropes in Persona fanfiction is 'alternate reality'. Writers like to explore what would happen if the events in the game took a different turn. In Highschool DxD, the 'rivalry' trope is common, especially between different devil clans. In a fanfiction that combines both, a trope could be 'culture shock'. A Persona character coming into the Highschool DxD world would experience a huge culture shock due to the different rules, species, and social structures. And also, the 'mentor - mentee' trope could be used. Maybe a powerful character from Persona becomes a mentor to a young devil in Highschool DxD, guiding them through their power - up journey.
Some popular tropes include the hero's journey. A young initiate in one of the factions starts on a path of self - discovery and ends up becoming a great hero. The 'lost technology' trope is also big. There are often stories about lost STC (Standard Template Construct) technology being rediscovered. And the trope of the secret alliance, where two unlikely factions secretly work together against a greater threat, like Chaos and the Imperium in some very specific and extreme circumstances.
One interesting plot could be the main character using their gaming skills to outwit the devils and angels in the Highschool DxD universe. For example, they might use strategic thinking from games to solve the complex power struggles and political intrigues in the story.