There are three explanations, and the explanations are as follows:
The first explanation: the word "maru" in ancient Japanese means "toilet" and "ward off evil spirits". The Japanese need to be lucky when they go fishing, so they name their ships various "maru". It turns out that the Japanese have been superstitious since ancient times. When they went fishing, the wind and waves were dangerous, and people often died in the belly of the fish. Therefore, the Japanese also liked to seek good luck, so they named the boat "Maru", which means "urinal". Using dirty things to ward off evil spirits is the most widely circulated and relatively the most reasonable one.
The second theory is that it is the homophony and transliteration of the Japanese word "_". In Japanese, the word "mill" is pronounced maro, and later evolved into the homophone word "maru" (pronounced maru) instead.
The third theory: Since the Heisei era in Japan, the Japanese have liked to name their own knives and their own dogs "a certain pill". The meaning of "an important item" later extended this habit to ships.
In short, the Japanese like to name ships "Maru", which is a cultural habit with a history of at least 800 years. As for the accurate allusion, there are many opinions and there is great controversy. However, 800 The allusions for many years have not been verified at the time of origin. The allusions have long been lost. Now it is very difficult to accurately verify them.