Lovey-Dovey Engagement - My Fiancé is 12 Years Older

Synopsis

"Koharu, you've had a fiancé since you were born..." This is what my grandfather confesses to me one day out of the blue. But how could I, a 25-year-old stranger to love, possibly have a fiancé? And on top of that, instead of living by myself while my grandfather is in the hospital, I have to live with him instead...?! He's tall, handsome, wealthy, and a CEO... not to mention 12 years my senior! We've got nothing in common! But his kindness and his unexpected naivete touch my heart, and before I know it...?! Between our short-term cohabitation and an marriage pact made by our grandfathers, this is one romance we can't let anyone find out about... (Source: MangaPlaza)