One is 'Future Diary'. It involves a battle royale where participants have diaries that can predict the future in different ways, much like the mind games in 'Death Note' with the power of the Death Note and the strategic thinking of Light and L. Another one could be 'Code Geass'. The main character, Lelouch, uses his Geass power to manipulate others and engage in complex strategic battles, similar to the mental duels in 'Death Note'.
There's 'Magi: The Labyrinth of Magic'. In this anime/manga, the characters often find themselves in complex situations where they have to use their wits to overcome challenges, whether it's dealing with powerful enemies or solving the mysteries of the labyrinths. It has elements of mind games like 'Death Note' where the characters need to think several steps ahead. Also, 'Log Horizon' has some similarities. The players in the game world have to use their strategic minds to survive and thrive, much like the strategic battles in 'Death Note' but in a different setting.
I'm not aware of many 'Death Note yaoi visual novel' games. However, 'Death Note' is a very popular franchise, but yaoi content might be more of a niche adaptation. There could be some fan - made or less - known works in this area, but it's not a mainstream type of game.
Ryuk would probably just be amused. He is a Shinigami who has seen a lot in his existence. Fanfiction is just another strange human creation to him. He might chuckle at some of the more outlandish ideas in the fanfictions, like a character having superpowers beyond the Death Note.
Misa would likely be excited. She is a big fan of Light and the whole 'Kira' concept. In fanfiction, if there are scenarios where she has more power or a closer relationship with Light, she would be all for it. However, she might also get jealous if there are other female characters getting too close to Light in the fanfictions.
Oh, for sure! Death Note is considered a masterpiece in the manga world. Its unique concept and the way it unfolds make it a must-read. The characters' development and the moral dilemmas presented make it stand out from the crowd.