There's also 'A Night with Subaru'. This one focuses on a single night where the reader and Subaru are alone in the mansion. The author does an excellent job of building tension and showing Subaru's more vulnerable side. It's a short but very engaging read that really delves into the relationship between the two characters.
A common theme is the struggle between Subaru's vampire nature and his feelings for the reader. For example, his vampiric instincts might make him act possessive at times.
One great place to find Diabolik Lovers Subaru x Reader fanfictions is Archive of Our Own (AO3). There are numerous well - written stories there. You can search by the tags 'Diabolik Lovers', 'Subaru x Reader' and sort by kudos or comments to find the popular and highly rated ones.
One interesting story could be where the reader is a new student at the school in the 'Diabolik Lovers' world and catches the attention of all the vampire brothers in different ways. Maybe one is initially hostile while another is overly curious.
There might be a fanfiction where Yui gets lost in a strange part of the vampire realm and Subaru is the only one who can find her. He battles his own inner demons as well as the external threats to rescue her. This story would show Subaru's protective side towards Yui.
There's a fanfiction titled 'Shadows of Understanding'. It shows how Shuu and Subaru might come to terms with their differences and develop a deeper connection. It has some really well - written dialogue that gives insights into their characters.
A frequent theme is the idea of redemption. They both have their flaws, and in many fanfictions, they try to make up for their past mistakes in relation to each other. There's also the theme of forbidden love, as their relationship is complex and not always accepted within the context of the 'diabolik lovers' world.
First, understand the characters. Subaru is a complex character, he's often moody and brooding. You need to capture his tsundere nature accurately. For the reader character, make them relatable. Start with an interesting encounter between them, like in a dark corridor of the vampire mansion. Then, build their relationship gradually. Don't rush the romance.
A more unique plot could be set in a modern human world where Subaru and Yui are trying to live a normal life. But Subaru's vampire nature keeps causing problems. They have to figure out how to deal with things like his need for blood in a world where vampires are not supposed to exist. This could lead to some really interesting and emotional moments between them as they struggle to be together.
Another interesting plot could be that Yui gets sick, and Subaru is the only one who can take care of her. He has to overcome his own insecurities and fears to be there for her. He might learn more about himself and his feelings for Yui during this time. As he nurses her back to health, their relationship deepens in a more tender and emotional way.
There's also 'Subaru's Redemption in Yui's Love'. This fanfic focuses on how Yui's love starts to heal Subaru's inner wounds. It has some really touching scenes where Subaru slowly opens up to Yui. The descriptions of their interactions are very vivid and it's a great read for fans of the pairing.