BMO! BMO's innocent and curious nature can be a great contrast to the more ethereal guardian angel. BMO might see the angel as a new friend or a mysterious being to explore. Also, Lady Rainicorn could be included. Her relationship with Jake and her ability to communicate in a different language can bring a new layer of complexity and charm to the fanfic, especially when she interacts with the guardian angel.
The Ice King could be really interesting. He's always up to something crazy, and his relationship with the guardian angel could be full of comical misunderstandings. Marceline the Vampire Queen is another character. Her dark past and her friendship with Finn and Jake can add depth to the fanfic when combined with the presence of the guardian angel. Plus, she has her own unique powers and personality that can create great storylines.
Ben Tennyson is definitely an interesting character to include. His ability to transform into different aliens gives a lot of possibilities for the story. Finn the Human is also great. His adventurous spirit and his sword - fighting skills can add action to the fanfiction. Jake the Dog can be really fun too, with his shape - shifting abilities. And of course, Princess Bubblegum, her intelligence and leadership can bring a different dynamic to the story.
You could write a fanfic where the guardian angel loses its powers for a while. This would create an interesting situation as it has to rely on the help of others in the Land of Ooo. It could also lead to character development as it discovers new things about itself and the world without its angelic abilities. Maybe it forms new friendships or realizes the true value of certain things.
Definitely Prince Gumball. His relationship with Fionna can add a lot of drama and interesting storylines. Also, Ice King. He can be both a comical and menacing presence. And of course, Marshall Lee. He has his own unique charm and his interactions with Fionna are always exciting.
Well, obviously Fionna and Cake themselves are very popular. Fionna is the main protagonist, a fearless adventurer girl, and Cake is her magical and sassy cat - sidekick. Prince Gumball is also a popular character to include. He can add a touch of royalty and his own brand of charm and mystery to the story. Ice King is another one. His zany and often misunderstood nature can bring a lot of humor and chaos to the fanfiction.
Finn, without a doubt. He is the hero of the story, always ready for a new adventure and to help those in need. Jake is also essential as his shape - shifting abilities add a lot of fun and creativity to the stories. Then there's the Ice King. His comical yet somewhat tragic nature makes him a really interesting character to write about. He can be both the villain and, at times, an unlikely ally in fanfiction.
Villains are also very popular in Angel Blade fanfiction. Characters who are after the power of the blade or those who oppose the wielder for ideological reasons. They create conflict and tension, driving the story forward. For instance, a powerful dark sorcerer who wants to corrupt the blade for his own evil deeds.
Buffy could be a great addition. Since she is Willow's best friend and has a complex relationship with Angel. Her presence could add some drama and tension, especially if there are unresolved feelings between her and Angel.
One of the most interesting characters to include is Nagato. His Rinnegan abilities and his connection to the Sage of Six Paths can create some really complex and exciting storylines in a Sennin Naruto fanfic. He could have some sort of interaction with Naruto's Sage Mode, perhaps teaching Naruto something new about the power of the Sages. Additionally, characters like Gaara can be interesting. His relationship with Naruto and his own unique powers can be incorporated into the fanfic in relation to Naruto's Sage Mode journey.
The leaders of different countries can be really interesting characters. They bring in their own political ideologies and leadership styles. For instance, the diplomatic and calm nature of some leaders can contrast with the more fiery and passionate ones. Their interactions could drive the story forward in many ways.
Issei himself is of course very interesting. His reactions to different time periods and how he uses his knowledge from the future can be really engaging. Then there's Rias. Her presence can add a layer of complexity, especially if she has different relationships with Issei in different timelines. Another interesting character could be Vali. His rivalry with Issei can take on new dimensions when time travel is involved, like competing in different historical battles or for the affections of a character in a different era.