Heart of a Samurai by Margi Preus

For a while the differences between life in America and life in Japan were always on Manjiro's mind. If only he could write! He would record the strange and wonderful things he observed in America. He would write it all in a letter to his mother, tuck it into an envelope, and stash it in the little box where he kept small treasures-the dozens of shells he had collected from all the places he'd been. Until then, he tucked his letters away in his memory.

Time is different here. There is no such thing as a tiger year, rat year, dragon year, and so on. There are twenty-four hours in a day and a year is divided into twelve months.