Isolation is also a theme. Monsters are usually isolated from society because of their differences. In the 'monster in love novel', the love relationship helps to break that isolation. For instance, in stories where a vampire falls in love with a human, they start to form a connection that bridges the gap between the vampire's solitary world and the human's social world.
Another theme is transformation. Often, the love between the two characters causes a transformation in the monster. It could be a physical transformation, like breaking a curse as in the classic fairy tales. Or it could be an emotional transformation, where the monster becomes more empathetic and loving.
One common theme could be acceptance. The idea of a monster finding love often involves the other characters in the novel having to accept the monster for who it is. Another theme might be the power of love to transform. Love could potentially change the nature or behavior of the monster. Also, the theme of outcast and belonging can be present. Since the monster is different, it may struggle with finding a place where it belongs, and love might be the key to that sense of belonging.
One common theme could be the exploration of the 'otherness'. The monster represents something different from the norm, and falling in love with it shows a break from conventional relationships. It might also deal with themes of acceptance, as the protagonist has to accept the monster for what it is. Another theme could be self - discovery. Through the relationship with the monster, the main character may learn more about themselves.
Another theme is the power of love to transform. The love between the two characters, one being a monster, often has the power to change the monster into a better version of itself. In many stories, the monster becomes more human - like in its emotions and behavior because of the love it receives.
One common theme is acceptance. In a love monster story, usually the human has to accept the monster's different appearance and nature, and the monster also has to accept the human's world. Another theme is transformation. The love often transforms the monster from being feared or alone to being more open and loving.
One common theme is the idea of acceptance. The non - human or'monster' character often has to be accepted by society or the human love interest. For example, in 'Beauty and the Beast', Belle has to look past the Beast's exterior and accept him for who he is inside. Another theme could be the power of love to transform. Love might change the monster's nature, like in some werewolf love stories where the love of a human can tame the beast within. Also, the theme of forbidden love often appears as society may not approve of a relationship between a human and a monster.
Since I cannot promote or discuss the erotic aspects, in general non - erotic monster love stories often have themes like acceptance. The human or other character has to accept the monster for who they are, with all their differences.
Survival is another big theme. In these novels, monsters often have to fight for their survival in a harsh environment. They need to evolve to better adapt. In 'Re:Monster', the goblin has to constantly improve himself to survive in a world full of stronger creatures.
Adventure is also a big theme. Since it's an isekai setting, there are often new lands to explore. In these novels, the character might go on quests to find rare monsters to breed or special items that can enhance their breeding abilities. It could be traveling through dangerous forests or ancient ruins. The exploration aspect adds a sense of excitement and discovery to the story.
One common theme is acceptance. The human protagonist often has to accept the differences of the monster girls in the harem. For example, in 'Monster Musume', the main character has to adapt to the unique cultures and physical traits of each monster girl.
Survival is a very common theme. Since the characters are often reborn as weak or low - level monsters, they have to fight to stay alive in a world full of stronger creatures. For example, in 'So I'm a Spider, So What?', the spider has to constantly find food and avoid being eaten.