I'm not really into that specific genre of fanfic, but you could try searching on popular fanfic websites like Archive of Our Own. They usually have a wide range of FNAF fanfics, and you might be able to find some that match your criteria by using their search filters.
One popular fnaf female springtrap fanfic is 'The Enigmatic Female Springtrap'. It has an interesting plot where the female Springtrap has unique interactions with the other animatronics. Another is 'Female Springtrap's Redemption' which focuses on her journey to overcome her past and find a new purpose in the haunted pizzeria. There's also 'A Female Springtrap's Tale' that delves into her backstory and how she came to be in the state she is.
The main character is, of course, the female Springtrap. She often has a complex personality, sometimes being menacing and other times showing a more vulnerable side. Other common characters include Freddy Fazbear, Bonnie, Chica, and Foxy. They interact with the female Springtrap in different ways, sometimes as enemies and other times as reluctant allies.
These fanfics usually focus on giving Izuku a younger appearance and exploring the new possibilities and challenges that come with it. They might change the dynamics of his relationships and his growth journey.
Well, the idea of the animatronics having a secret society or a code among themselves can be really interesting in non - adult FNAF 2 fanfics. Also, the concept of the pizzeria having hidden passages or secrets that the characters discover as they try to stay alive during the nights. Some fanfics might also focus on the psychological impact on the characters of being in such a spooky place, like the security guards' nightmares and how they cope with the fear.
The main plots usually revolve around Thor being de-aged and his adventures in this new form. Maybe there's a quest to regain his original age or he has to adapt to a younger body in the modern world.
One common theme is the idea of redemption. The Puppet, which is often seen as a somewhat malevolent figure in the FNAF world, might be redeemed through its love for Jeremy. It could be that the love changes the Puppet's nature and makes it more benevolent. Another theme is the power of love against all odds. In the spooky and dangerous world of FNAF, a love between a guard like Jeremy and a strange entity like the Puppet is unexpected and goes against the norm, but it still manages to thrive.
Well, 'Joseph's Second Chance' is a notable one. It has a well-crafted story where the de-aged Joseph faces new challenges and grows in interesting ways. The author does a great job of maintaining the essence of the character while exploring this new age dynamic.
There's this one called 'Hamilton's Youthful Adventures' that's quite popular. It's got a fresh take on Hamilton's early years and the challenges he faced.