From DrCoke at MangaHelpers:
Japan's population is becoming older. With the advances in medicine and technology, the average age of an individual has steadily risen, but the birth rate has dropped significantly since the "baby boomer" generation. This leads to a natural imbalance between the elderly versus the younger, working class population. What becomes necessary are people like Onda Momotaro to nurse the elderly gentlemen and ladies that are becoming increasingly senile.

His introduction into the "industry" of taking care of the elderly was shocking. What he saw was an elderly man being tied down to a bed for his own safety, while the nurses and caretakers consider this a "necessary evil." Momotaro is determined to help the elderly and bring back their smiles.