Otome Game no Mob Nanoni, Naze ka Oshi ni Ai wo Sasayakarete Imasu!

https://www.cmoa.jp/title/319011/ The protagonist, who was supposed to be lying sick in bed, is reincarnated as the daughter of a count, Lilibelle. Using the knowledge from her previous life, she enjoys peaceful and happy days… but something is missing! However, upon attending a certain tea party and hearing a particular voice, she realizes: "This is the world of the otome game I mastered in my previous life! And that voice… it’s my ultimate favorite, Allen-sama!!!" Having regained the love she was missing for her favorite, she also understands that she is just a background character in this world. Being able to watch Allen-sama grow as a side character… what a dream! But then, Allen-sama proposes marriage to her――!?