One possible reason could be that the Houndoom has a strong bond with the girl. In many fanfics, animals or Pokémon can form deep emotional connections with humans. Maybe the Houndoom was rescued by the girl, and this licking is a sign of gratitude and affection.
Perhaps in the fanfic's world, Houndoom's are known to show dominance or acceptance in this way. If the girl has just entered the Houndoom's territory or joined a group that the Houndoom is part of, the lick could be a way of saying 'you're okay in my world'.
It might be part of a magical or special ability situation. For example, the Houndoom's lick could have some sort of healing or power - transferring property. So it licks the girl's face to give her some of its energy or to heal her from an injury or illness.
Perhaps the werewolf has a connection to the girl from a past event. It could be that the girl once saved the werewolf in its human form, and now in its werewolf state, it recognizes her and is showing gratitude by licking her face. This could lead to a story of loyalty and protection, with the werewolf becoming the girl's guardian.
One possible plot could be that the girl is lost in a forest where the giant werewolf lives. At first, she's terrified, but as the werewolf licks her face, she realizes it's not being aggressive. Maybe the werewolf has some kind of special connection to her, like it senses she's pure of heart or has some latent power. And through this face - licking encounter, a bond begins to form between them, leading to a series of adventures where they protect the forest together.
One significance could be to show innocence. The act of the dog licking is a very pure form of showing affection, so it might be used to highlight the girl's purity or the simple, uncomplicated relationship between them.
In the fanfic, the giant dog face licking the micro girl could be a comical situation. Suppose the dog is overly enthusiastic and doesn't realize its own size compared to the girl. The girl might initially be startled but then come to understand that the dog means no harm. This could lead to a series of adventures where the dog and the girl become an unlikely duo, with the licking being a recurring and endearing part of their relationship.
Maybe in a magical world fanfic, the girl is a fairy and she encounters a strange little creature. The creature, thinking she is a friend, licks her face as a sign of greeting. This event then sets off a series of adventures as the girl tries to figure out what the creature is and what it wants.
One possibility could be a heartwarming story where the mastiff, being friendly and affectionate, licks the girl as a form of greeting. Maybe the girl has just come home from a long day and the mastiff's excited licks cheer her up.
It could signify deep affection. Just like in real life, dogs show love by licking, so in a fanfic, it might be a way to show that the dog has a strong bond with the girl.
One possible plot could be that a girl is lost in the forest and a Growlithe finds her. Instead of being aggressive, the Growlithe shows friendliness by gently licking her face. This simple act could be the start of a beautiful friendship where the girl and the Growlithe explore the forest together and help each other out in various situations.
One possible plot could be that the girl is in a magical realm where she encounters a dragon. At first, she's frightened, but the dragon shows some sort of strange affection towards her. The licking could be a way for the dragon to show its interest or a form of greeting in the context of this fictional world.
One possibility could be that the grizzly dog in the fanfic is a magical or enchanted creature. The girl might be lost in the forest where the grizzly dog lives. The dog, sensing her fear and confusion, approaches her gently and licks her face as a sign of friendliness. This could be the start of an adventure where the girl and the dog form an unlikely bond and they go on to face various challenges together in the forest.