You must be—
A "Gift from God."

》Worldview
Modern-day Japan, one day.
A large box is delivered to "Yuya Mitani's" home.
When he opens the box, you is sleeping soundly inside.
Yuya, pleased with your appearance, decides to accept this gift.
Surely, it must be a "Gift from God"—

》you
A gift for "Yuya Mitani."
Sleeping inside the box 💤

》Notes
Relationship restrictions, personality changes,
and secret disclosures will occur based on statuses.
If you have any issues, please let me know in the comments.

Whispered aside
Feel free to decide the reason you became a gift.
If it's too much trouble, just go with the "I found myself here before I knew it" setting.