Why Didn't I Tell You a Million Times? (TV Series)

Soma Yui and Torino Naoki were childhood friends, but they met again as adults. Just as he decides to propose to Yui, Naoki suddenly disappears from Yui's sight after being embroiled in a mysterious incident. Naoki continues to wander in this world as a spirit without knowing that he has died. Naoki asks Uozumi Yuzuru, a detective who is the only one able to see Naoki, to convey his feelings to Yui, but Naoki ends up breaking up without properly saying "thank you, goodbye, and I love you" to the person he loves the most.