Ghoulia Yelps could be another one. She is really into zombie and horror - related things. The FNAF characters are very much in that horror genre. Ghoulia might be able to use her knowledge of horror to find a way to co - exist with the animatronics or even find a common ground. She could communicate in her own unique way and perhaps teach the FNAF characters a thing or two about Monster High.
Frankie Stein might also interact well. Frankie is always curious about new things and how they work. The FNAF animatronics with their mechanical and somewhat mysterious workings would be right up Frankie's alley. Frankie would probably try to study them and figure out how to make them less menacing, or at least understand their purpose.
Armin could be another good character for this. He's intelligent and good at strategizing. In a 'Attack on Titan meets FNAF' fanfiction, he could use his wits to try and understand the nature of the FNAF elements and come up with plans to either avoid or combat the threats that come from the combination of the two universes.
Probably Leonardo from the Turtles and Freddy Fazbear. Leonardo is the leader, so he would likely be the first to step forward and assess the situation when they encounter the FNAF animatronics. Freddy, being the main animatronic, would also be in the forefront. Their personalities are quite different, with Leonardo being more disciplined and Freddy having a more mysterious and somewhat menacing presence. Their first interaction could be a tense stand - off as they try to figure out each other's intentions.
Hermione would be a great candidate. Her thirst for knowledge and eagerness to learn about different forms of magic would make her very interested in Dante Vale and his skills. She would probably bombard him with questions and they could have long discussions about magic.
Hermione would be a likely candidate. Hermione is intelligent and curious. She would be fascinated by Harley Quinn's out - of - the - box thinking and her unique way of approaching problems. She might try to study Harley's psychology while also trying to keep her out of trouble in the wizarding world.
Death from DarkSiders and Black Widow could have an interesting interaction. Death has seen countless deaths and has a very different perspective on life and death compared to the human Black Widow. Their conversations could be deep and thought - provoking as they work together on a mission.
I think Mirabel from Encanto and Aang from Avatar would be likely to interact. Mirabel is all about finding her place in the family and Aang is on a journey to save the world. They could share their experiences of feeling different and having big responsibilities.
Kakashi could also be a character involved in interactions. His calm and observant nature would make him a good mediator between the two groups. He might be interested in learning about the monster musume's abilities and how they could potentially be used in the ninja world. Rock Lee might also be a candidate. His enthusiasm and determination could be an interesting contrast to the monster musume, and he could potentially learn new fighting styles from them or teach them his own.
Richard. His business acumen and knowledge of politics could be very useful in the Stark world. He could advise the Starks on economic matters and trade deals. He might also be intrigued by the feudal system and try to find ways to improve it, while at the same time sharing some of his wisdom about leadership and education with the Stark children.
Luna could also be a great character to interact with Casper. Given her love for all things cool and different, she would probably be really excited to meet a friendly ghost. She might even write a song about their encounter.
Percy himself, of course. Given his leadership skills and powerful abilities, he would be the first to step up and face the Pillar Men. His ability to control water could be a great asset or a hindrance depending on the situation.