#Motonari's birthday was actually the 16th.

[heartofbasara-blog]

Izanagi heard it was his dear son's birthday, and upon summoning him, he gives Motonari a large gilded, golden egg. He smiles, promising it will hatch into something wonderful soon, as long as Motonari takes care of it.

His eyes grow wide as he is given such a gift from his godly adoptive father.  He analyzes the golden egg carefully, and hearing that it would hatch into something soon made his eyes glow with interest.  He looks up at the god, a small blush on his face as he thanks him, appreciative.  This…this meant a lot to him.