Tensei Idol to Doruota no Kishi

After several reincarnations, Takao, a former knight, is now living as an office worker in modern Japan. After discovering Hikaru is the reincarnation of the prince he served but unable to save in his past life, he swore to protect Hikaru in this life by being a hardcore fan.
For the sake of protecting Hikaru from a closer position, Takao decides to become his manager. But after Hikaru, who seems more aloof compared to their past lives, seems to have a special smile only for him, Takao starts to have another type of feeling budding within him!

(Source: Daria Comics, translated)