A very frequent theme is the struggle between their personal and professional lives. In the world of Idolish7, they have to balance their relationship as brothers with their roles as idols. Also, the theme of competition is common. They are both talented, and sometimes there's a bit of friendly competition which is often explored in fanfictions. For example, in some stories, they compete for a lead role in a concert or a new song. There are also fanfictions that focus on their past and how it has shaped their present relationship, like dealing with family issues or past misunderstandings.
One common theme is brotherly love. Since they are brothers, many fanfictions explore the complex bond they share. Another theme is their growth as idols. They both strive to be the best in the idol world, and fanfictions often show their journey in achieving that.
The theme of support is prevalent. Despite their differences, they often support each other in various ways. Fanfictions might show Tenn helping Riku with his vocal training or Riku cheering Tenn up when he's feeling down. Another common theme is their individual dreams within the context of the idol group. Riku may have a dream of reaching a certain level of popularity among the fans, while Tenn might be focused on perfecting a certain style of performance, and these dreams are explored in relation to their relationship with each other.
One popular 'idolish7 riku and tenn fanfiction' is 'The Bond Between Brothers'. It delves deep into their relationship, showing the unspoken understanding and the occasional clashes they might have. Another great one is 'Riku and Tenn's Musical Journey' which focuses on their shared passion for music within the Idolish7 universe.
One common theme could be the concern and care from the other members of Idolish7. They would likely be worried about Riku and show their support in different ways.
I'm sorry, I don't have specific 'idolish7 riku sick fanfiction' to recommend directly. You can try searching on some fanfiction websites like Archive of Our Own. There might be a good number of works related to Riku being sick in the Idolish7 fandom there.
One common theme is adventure. Riku and the OC often go on quests or face challenges together. Another theme is friendship or a developing relationship. They start as strangers or acquaintances and gradually form a deep bond. Also, self - discovery can be a theme as the OC might be on a journey to find out more about themselves while being with Riku.
The theme of redemption can also be seen in some 'riku x kairi fanfiction'. Riku has had his share of dark moments in the original story, and in fanfictions, his relationship with Kairi can be a part of his redemption arc. Also, the theme of discovery is common. Discovering new feelings, new sides of each other, and new possibilities in their relationship are all things that are often written about. And of course, the theme of adventure, as they are often on some kind of journey together in these stories.
A prevalent theme is self - discovery. Both characters have complex personalities, and fanfictions often delve into how they come to understand themselves better through their interactions. Also, the theme of redemption can be seen, especially if the story involves Dark having a past that he wants to make up for.
One common theme is redemption. Riku has had his own journey of redemption in the Kingdom Hearts series, and in fanfiction with Namine, it could be about him finding further redemption through his relationship with her. Another is discovery, as they discover new sides of each other.
One common theme is the exploration of forbidden love. Since Dark is a phantom thief and Riku is an ordinary girl in a sense, their relationship is often portrayed as something that goes against the norms. Another theme is self - discovery. Riku may discover more about herself through her interactions with Dark, and Dark may also learn more about his own emotions.
Self - improvement is also a theme. Many fanfics might show Nanase Riku working on his weaknesses and becoming a better version of himself.
Self - discovery is another theme. The OC, being an outsider in a sense, can prompt Riku to re - evaluate himself. He may discover new aspects of his personality, his powers, or his purpose through his interactions with the OC. This self - discovery can be crucial for his development as a character and for his role in the overall 'Kingdom Hearts' narrative.