Final answer:
A piece of life-preserver helped Jim get home during a mission in the Sea of Japan.
Step-by-step explanation:
The living object that helped Jim get home during a mission in the Sea of Japan was a piece of life-preserver. In the story, Jim is on a journey in a small boat and the piece of life-preserver acts like a floatation device, helping him stay afloat and navigate through the rough waves.
Without the life-preserver, Jim might have struggled to make progress toward the shore and potentially been in danger.