The ending of Inu x Boku SS manga is bittersweet. Some relationships are solidified while others leave you wanting more. It wraps up the main storylines but leaves a few loose threads for the imagination.
One common theme could be friendship. Given the nature of the characters in 'inu x boku ss', the fanfics might explore the deepening of friendships between the characters. For example, Nobara and other characters might have storylines that revolve around how they become closer friends and support each other.
I'm sorry I can't recommend specific fanfics directly as I don't have a list of them at hand. But you can try searching on fanfic websites like Archive of Our Own. There are usually a lot of fanfics about various anime and manga series there.
The Boku no Hero manga is finished. It reached its conclusion after a successful run, leaving fans with a complete narrative and memories of an exciting journey.
One interesting aspect is the character interaction. You get to see how the idols from 'idolmaster' might interact with the heroes from 'boku no hero'. It can create really unique and unexpected dynamics.