The Bat - family would be at the forefront. They have a deep connection with Batman. Then there are the other heroes from the DC universe. Superman would likely come to show his respect for his friend and fellow hero. Wonder Woman might also be there, as she and Batman have worked together on many occasions. Additionally, some of the reformed villains who had a begrudging respect for Batman could also make an appearance, like Catwoman. And let's not forget the people of Gotham. Some of the ordinary citizens who Batman has saved over the years might come to the funeral to pay their last respects.
Definitely the Bat - family. Robin, Nightwing, Batgirl, etc. would be there to pay their respects. Alfred, who has been like a father figure to Batman, would also be present. And of course, Commissioner Gordon, as he has been Batman's ally in the fight against crime in Gotham for a long time.
Alfred is always a likely ally. His knowledge and experience can provide valuable support to Batman. Also, Oracle (Barbara Gordon) could be an important ally, using her hacking skills to disrupt any technology Superman might use or to gather information.
Ra's al Ghul could be a great villain. He is always seeking power and immortality. In a crossover, he might see the potential in mutant genes to achieve his goals. His vast resources and knowledge would make him a formidable foe for both Wolverine and Batman. He could be plotting to use mutants in some grand scheme that would also impact Gotham, which would draw the attention of both heroes.
Black Widow. She has a lot in common with Batman in terms of skills. Both are highly trained in combat, stealth, and espionage. They would understand each other's need for secrecy and their ability to operate in the shadows.
Obviously, her crewmates from the Normandy. Garrus would be there, being one of her closest friends. Tali too, as they had a strong bond. Liara would also attend, given her connection to Shepard.
The Scooby Gang as a whole would be severely affected. They were a tight - knit group led by Buffy. Without her, they'd have to re - evaluate their roles and dynamics. They might argue about how to move forward, with some wanting to continue in Buffy's footsteps and others being too grief - stricken to think about fighting evil. This would create a lot of tension and character development within the fanfic.
Sasuke would be one of the most affected. He and Naruto had a complex relationship, from being rivals to friends. Naruto's death would leave a huge void in Sasuke's life. Also, Hinata. She loves Naruto deeply, and losing him would be devastating for her.
Iron Man. They both are very intelligent and rely on their technology a great deal. They could share ideas about improving their gadgets and suits.
Iron Man and Batman might be the most likely to clash. Iron Man is all about high - tech and showing off his latest inventions. Batman, while also using technology, is more of a brooding, solitary figure. Iron Man might see Batman as a bit of a relic or too old - fashioned in his methods. Batman, in turn, could view Iron Man as a bit too flashy and irresponsible with his power. Their egos could get in the way of them working together initially.
Harley Quinn is an obvious choice. Her obsessive love for the Joker could be transferred to Batman in a fanfiction harem scenario. She's unpredictable and could add a lot of chaos and humor to the group. Then there's Poison Ivy. Her connection to nature and her alluring charm would make her a likely candidate. She could use her plants to protect the harem or create a private sanctuary for them.
There could be a wide range of people, including comic book fans, cosplayers, and celebrities related to the comic and entertainment industry.