Artemis could be a great addition. He could offer some wise advice and be a sort of mentor figure to them. His knowledge of the magical world could help the trio in their adventures.
Pluto could be included as well. Given her power over time and space, she could bring in some really cool plot elements. For example, she could send the trio back in time to fix a mistake that is causing problems in their present world.
You can try fanfiction websites like Archive of Our Own (AO3). It has a large collection of various fanfictions, including those related to Haruka x Usagi x Michiru. Just search for the relevant tags, and you'll likely find a good number of stories.
Well, 'The Harmonious Trio' is a great fanfiction. It starts by introducing their individual personalities. Haruka's cool and confident demeanor, Usagi's kind - hearted and sometimes clumsy nature, and Michiru's elegant and mysterious presence. As the story progresses, it shows how they come together. They face a common enemy that tries to break their bond, but instead, it only makes them stronger. It's a long - form fanfiction that really dives into their relationships and character development.
Perhaps a story set in an alternate universe where they are all part of a special task force. Haruka is the fearless leader, Michiru is the strategist, and Usagi is the heart of the group. They face many challenges from enemy forces and their relationships evolve as they fight side by side.
These two could be from a specific fandom. They are characters that the fanfiction author has chosen to focus on. Michiru's love for Haruka in a tux could be a unique take on their relationship. Maybe they are part of a group of characters in their original story, but here, the fanfiction delves into their individual relationship, with the tuxedo being a significant symbol of attraction for Michiru towards Haruka.
There's 'A Glimpse of Eternity' which is also quite good. It focuses on the more tender and private aspects of their relationship. The author does a great job of painting a vivid picture of their love and the small, everyday moments that make their bond so special.
Grandpa Max would be a great addition. His experience and wisdom could be a guiding force for Gwen and Lemon. Also, Kevin Levin could be included. His powers and his complex relationship with Ben could add an interesting dynamic to the story. Another good character could be Rook. His loyalty and combat skills could be useful in any adventures that Gwen and Lemon get into.
Ain would also be interesting. His mysterious past and his unique abilities could add a new layer of complexity to the story. He might be an ally or an unexpected foe, and his interactions with Elsword and Elesis could lead to some intense plot twists. Maybe he has some hidden knowledge about their destinies that he reveals gradually.
Harley Quinn could be a great addition. She has a complex relationship with both Poison Ivy and Batman. Her chaotic nature could add a lot of twists to the story. Another character could be Alfred. His wisdom and loyalty to Batman could provide interesting interactions when dealing with Ivy.
I think Hinata would be an interesting character to include. She has her own unrequited love for Naruto. Her presence could add some drama to the story as she sees Naruto getting closer to Ahri. Another good character could be Jiraiya. His lecherous yet knowledgeable self could provide some comical relief and also give some sage advice to Naruto and Ahri when they need it.
The Medic could be a great addition. He could be the one patching up the Sniper and Spy when they get injured during their adventures. His medical knowledge and sometimes wacky personality could add some interesting comedic or tense moments. For example, when the Sniper is badly wounded, the Medic has to perform a risky procedure while the Spy is keeping watch and fending off potential threats.