Can you recommend some similar light novels like 'Monster Duchess and Contract Princess'?

Another theme could be friendship or alliance. Since they have a contract, they are bound in some way, and through this connection, themes of loyalty, trust, and building a relationship despite their differences are likely to be explored. For example, they might have to rely on each other in a world full of challenges and enemies. Also, the idea of acceptance of the other's 'monstrous' or different nature could be a theme as well.

Well, in 'Monster Duchess and Contract Princess' manhwa, there's a complex web of relationships and quests. The duchess and princess face various obstacles together, and their bond grows stronger as they navigate this magical realm full of secrets and perils.

The storylines can vary too. Maybe the manga has more subplots or takes a different direction with certain events compared to the other. Also, the art style could have distinct features that set them apart.

One similar light novel could be 'My Youth Romantic Comedy Is Wrong, As I Expected'. It also has complex characters and an engaging plot. Another is 'Re:Zero − Starting Life in Another World', which has a unique take on the isekai genre like 'Sweetest Monster Light Novel' might. And 'The Rising of the Shield Hero' is also a great choice with its own interesting world - building and character development.

There are several light novels that might be similar. 'Snowflake Princess' is one. It has a similar concept of a princess in a unique world, just like in 'Milk Princess Light Novel'. The story is filled with magic and the growth of the princess. Another one is 'Sunflower Girl Light Novel' which has elements of a girl's adventure and her relationship with the world around her. And 'Daisy Princess' also has a comparable theme of a young female character in a somewhat magical and story - rich setting.

I'm afraid I don't know about this 'Duchess Slims Husband' light novel. But you can look for it in libraries that have a good collection of light novels from different regions. Some libraries also have online catalogs where you can search for such specific titles.

One similar light novel could be 'Haganai: I Don't Have Many Friends'. It also features unique character relationships and a bit of a different take on social situations within a fictional setting. Another one might be 'My Youth Romantic Comedy Is Wrong, As I Expected', which has complex character dynamics and a story that unfolds in a school setting.

One similar light novel could be 'The Ascendance of a Bookworm'. It also features a strong - willed female lead in a unique world setting. Another is 'Sword Art Online' which has an interesting plot and character development. And 'Re:Zero − Starting Life in Another World' is also great as it has a complex story line.

There's also 'Sword Art Online'. While not exactly the same, it has a protagonist in a virtual world with unique challenges and growth. The main character has to adapt to a new environment and overcome various obstacles, much like in 'At Night I Become a Monster'.

One similar light novel could be 'The Apothecary Diaries'. It also has a female protagonist in a historical - like setting dealing with medical and court - related matters. Another is 'Ascendance of a Bookworm' which involves a girl using her knowledge in a new world, and there are elements of medicine and self - improvement.