Golden Sun: Dark Dawn. It is acquired by talking to an old woman in a house in Kaocho; she asks the player if they mind delivering this parcel to her granddaughter in Sana. When taken to Tonfon, and after using Insight on the girl on the main bridge, you can give the parcel to the girl. She gives you a Psy Crystal as a thank you upon trying to exit Tonfon and also gives you a present to take back to the old woman in Kaocho. When doing this, use Spirit Sense on the corpse of the now dead woman and she will be relieved and joyed to hear such love from her grand child and her soul can finally rest in peace. If you interact with the present left on the floor, you can receive the Ninja Sandals. However, you MUST take the Grandmother's Gift BEFORE the Grave Eclipse, because such eclipse is when the old woman dies.
As a key item, the Grandmother's Gift cannot be sold or dropped.