I'm not sure about the exact plot as I haven't read it in detail. But generally, it might involve the adventures of Sera in a world related to the Royal Stars.
I'm not sure specifically as I haven't played it. But generally, a visual novel often involves a story with characters, and perhaps in 'the royal seven stars visual novel' it might be about the adventures or relationships among a group of characters related to the so - called 'royal seven stars'.
I'm not entirely sure specifically about a 'sera yaoi visual novel' as it could be a relatively unknown or niche title. It might be a visual novel that features yaoi themes. Yaoi typically involves romantic or sexual relationships between male characters.
I'm not entirely sure as I haven't read it specifically. But generally, a graphic novel set in a 'royal city' might be about the power struggles, the lives of the royalty, the social hierarchy, and the daily goings - on in such a city. It could also involve some sort of adventure or mystery within the context of this royal setting.
I'm not aware of any specifically named'sera yaoi visual novel' being extremely popular. There are many yaoi - themed visual novels in general, but not one that I know of with this exact name in the mainstream.
Since I don't know the exact 'rock stars graphic novel' you're referring to, it could cover a vast range of topics. It might tell the story of a particular rock star's journey from being an unknown musician to a global icon. It could depict the backstage drama, the relationships within the band, the struggles with record labels, and how they interact with their fans. It could also be a more fantastical take on the rock star world, where there are elements of magic or alternate realities related to the music scene.