Why didn't I tell you a million times

When childhood friends Yui and Naoki are by chance reunited as adults, they begin to feel they were destined for each other. However, just as Naoki prepares to propose to Yui, he becomes embroiled in a mysterious incident and dies.

Now Naoki's soul wanders the world unable to express his true feelings for Yui. Yuzuru, a detective and the only person who can see Naoki, goes in pursuit of the truth behind Naoki’s death. At Naoki tries to use Yuzuru to talk to Yui, but will he be able to convey his message of love?