Un samouraï au Vatican

Why do 600 inhabitants of the small southern Spanish town of Coria del Río bear the surname "Japón"? It is the legacy of an unusual expedition that took place 400 years ago: In October 1613, the samurai Hasekura Tsunenaga boarded the galleon "San Juan Bautista" on behalf of the ruler Date Masamune in Sendai, Japan. In addition to merchants, warriors and Spanish sailors, the Spanish Franciscan monk Luis Sotelo, who spoke fluent Japanese, also embarked. The legation wanted to obtain permission from the Spanish King Philip III and Pope Paul V to open a new sea route to India alongside the spice route; in return, Christian missionaries were to be sent to Japan. When he set off, Hasekura Tsunenaga had no idea that the journey would take seven years. Who was this Japanese samurai? What is known about his motives and what is known about the actual background to the expedition?