One common theme is alternate universes. Writers like to explore what would happen if certain events in the original series had gone differently. For example, what if Lelouch had made different choices during his battles or negotiations.
I'm not specifically familiar with 'Marianne vi Britannia' light novels. It could be a rather niche or new series. You might try searching for it in specialized light novel databases or forums to find out more about popular ones in this category.
Some dedicated anime forums might also be a good place to look for Code Geass Lelouch vi Britannia fanfics. For example, Anime-Planet has a community section where fans might share or recommend their favorite fan-written stories. Additionally, Reddit has subreddits related to Code Geass where you can ask for fanfic suggestions.
You could start by looking in local bookstores that have a section dedicated to light novels. Some larger chain bookstores might carry them if they are widely available.
In many fanfictions about Light Yagami and Misa, their relationship is often complex. Light initially uses Misa for his own ends in the 'Death Note' story. He manipulates her feelings because of her Shinigami eyes which are useful for his plan to create a new world. Misa, on the other hand, is blindly in love with Light. In fanfiction, this dynamic can be explored in different ways. Some might show Misa slowly realizing she's being used, while others may focus on a more 'romanticized' version of their relationship where Light actually develops some real feelings for Misa.
I'm not sure specifically which 'Kazuma Yagami' in a light novel as the name is not widely known in extremely popular mainstream light novels. It could be a character from a relatively niche or new light novel series.
There are a vast number of fanfics on the internet, and given the creativity of the fan community, it's very possible that there are fanfics portraying Light Yagami as gay. Fanfic writers often take characters from their favorite shows or books and put them in new and different situations, including changing their sexual orientation to tell a different kind of story. These fanfics can range from being well - written and thought - provoking to just being a bit of fun and experimentation. So, if you look hard enough on the right fanfic websites, you may come across one.
Light Yagami's death in the manga occurs because Ryuk, the shinigami who gave him the Death Note, decides to end his life. It's a result of Light's descent into madness and his attempts to evade justice.
Another theme is the re - imagining of relationships. In the original story, Light has certain relationships with characters like L and Misa. In the fanfics with a female Light, these relationships are often re - evaluated. Maybe female Light has a more complex relationship with L as they try to outwit each other, and her relationship with Misa could be more of a sisterly rivalry or a different form of alliance.
One unique aspect is the clash of different moral systems. For example, when Light crosses into a universe like 'Star Trek' where the Federation has a very different view on life and justice. His use of the Death Note would be highly controversial. Another aspect is the exploration of his character in new settings. In a crossover with 'Fullmetal Alchemist', he would be exposed to a world full of alchemy and different power structures.