Another theme is friendship or alliance building. They might start as strangers, but as they face various challenges together, like fighting demons or exploring new lands, they form a bond. It could be that the OC has a special ability that Sesshomaru needs for his own goals, or vice versa. This creates a situation where they have to work together and trust each other.
One common theme is the journey of self - discovery. The OC often enters Sesshomaru's world and in the process, both characters learn more about themselves. For example, the OC might be a human who has to adapt to the dangerous and magical world of Sesshomaru, and Sesshomaru might learn about the value of human emotions through the OC.
The theme of redemption can also be present. Maybe Sesshomaru has made some mistakes in his past, and the OC, with their different perspective, helps him see a new way forward. Or the OC has their own past to overcome, and Sesshomaru, in his own cold but sometimes helpful way, aids the OC in their journey of redemption. These themes add depth to the relationship between Sesshomaru and the OC in the fanfiction.
One common theme is friendship. The OC can be a new friend to Kagome in the feudal era, helping her adapt to the strange world she's in. Another theme is adventure. They might embark on quests together to find powerful artifacts or defeat demons. For example, they could search for a magical jewel that has the power to restore peace to the land.
One theme could be the clash of their two worlds. Kagome is from the modern world and Sesshomaru is from the feudal demon - filled world. Stories might explore how they bridge this gap, like Kagome introducing modern concepts to Sesshomaru or Sesshomaru showing Kagome the secrets of the demon world. This can be a theme that exists even without the 'dark lemon' elements.
Adventure is also a big theme. The male OC and Sasuke could go on quests together, facing various challenges like battling powerful enemies or exploring mysterious lands. This allows for a lot of character growth for both of them. Another theme could be redemption. If the male OC has a troubled past, Sasuke's own journey of redemption can be paralleled or even help the OC in his own path of self - discovery, which can make for a very engaging story.
One common theme is the struggle of an ordinary oc becoming worthy of a powerful being like Sesshomaru. It often involves the oc having to prove themselves, either through strength or some other special quality.
Love and redemption are also prevalent themes. Sesshomaru may be seen as a cold and aloof character at first, but through his relationship with the si oc, he may experience a change of heart. The si oc might also find redemption in their own way, perhaps by helping Sesshomaru or the people in the Inuyasha world. This theme adds a lot of depth to the stories.
One common theme is friendship. South Italy might be shown forming a deep and unique friendship with the OC. Another theme could be cultural exchange. Since Hetalia is all about different countries' personifications, the OC could learn about Italian culture from South Italy and vice versa.
Another theme is the exploration of power. The OC usually has some unique power or ability, and how Sesshomaru reacts to it is a big part of the story. Sometimes they might have a power struggle, or they might learn from each other's powers.
One common theme is the power dynamic. Since Sesshomaru is a very powerful demon, often the OC has to find their place in relation to his power. It could be that the OC is initially in awe or in conflict with his power. Another theme is the exploration of the Inuyasha universe. The fanfic usually uses the setting and lore of the Inuyasha world, and the OC gets to experience it, whether it's the different demons, magic, or the feudal Japan - like setting.
One common theme is the journey of self - discovery for Sesshomaru. The OC's pregnancy forces him to look at himself and his place in the world in a new light. Another theme is the protection of the unborn child. Sesshomaru, being a powerful character, will go to great lengths to keep the OC and the baby safe.
Well, the theme of redemption can be quite common. The male oc may have a past he's not proud of, and Sesshomaru's presence helps him on the path to redemption. Or vice versa, Sesshomaru might find himself changing for the better. Another theme is the struggle against a common enemy. They have to put aside their differences and work together. And also, the theme of loyalty often comes up. Once they form a bond, they are loyal to each other through thick and thin.