Well, without having read the 'fenrir kaasan to attaka gohan light novel', it's difficult to say precisely. But given the name, perhaps Fenrir is a central character, maybe a mother figure (kaasan in Japanese). And attaka gohan could be something important in the plot, like a magical or very special meal that drives the story forward in some way.
You might try looking for it in specialized Japanese light novel stores, either physical ones if you can find them, or online stores that sell a wide range of light novels.
Since I'm not familiar with this particular light novel, it's all speculation. But generally, in Japanese light novels, the title often gives clues about the main elements of the story. 'Fenrir' might be a non - human character, perhaps a mythological being. 'Kaasan' being mother, it could imply a family - centered plot. And 'attakago meshi' which is related to food, might suggest that food is a key part of the story, whether it's about cooking together, a food - related quest, or a special meal that has significance in the relationship between the characters.
Well, it might be good because it could have an interesting take on the characters of Hermione and Fenrir. Maybe it explores their relationship in a unique way that we haven't seen before in the original works.
Sorry, I'm not really sure of any specific ones similar to it off the top of my head. But you could try searching on fanfiction platforms using tags related to Hermione, Fenrir, and the genre of the original story it's based on.
In this fanfiction, their relationship could transform in a significant way. At first, they may have been more like acquaintances or even rivals among werewolves. But with Harry in the picture, they would be forced to communicate better. Remus could influence Fenrir to be more civilized, while Fenrir could make Remus more assertive. They would share the joys and sorrows of raising Harry, which would create a bond between them that was stronger than just their werewolf connection.
In many such fanfictions, Hermione might start by trying to understand Fenrir's situation from a research perspective. She could be using her extensive knowledge of magic and werewolves to figure out a way to help him. For example, she might look into any spells or potions that could ease his lycanthropy symptoms.
It could be other Death Eaters. They might suspect that Fenrir is up to something with Hermione and try to stop him. For example, Bellatrix Lestrange could be a major antagonist. She's known for her cruelty and loyalty to Voldemort, and she might not trust Fenrir's actions regarding Hermione.
Well, in this kind of fanfiction, Fenrir might be protective of Harry perhaps because he sees something special in Harry. Maybe he has his own reasons that are different from the normal perception of their relationship in the original works. It could be that Fenrir has a change of heart or there are some hidden plot elements that make him want to safeguard Harry.