LindaL100

and Mamoru often calls Usagi "Usako", it's an endearing nickname he gave her which literally means "bunny child" in japanese.

Another fun fact is that each of the Sailor senshis civilian names in Japanese literally has their corresponding elements, for example Sailor Moon's civilian name "Tsukino Usagi", the word "tsuki" in "Tsukino" literally means moon in Japanese, and in Japanese mythology it is said that a bunny lives on the moon, hence Usagi's name literally means "bunny of the moon" in Japanese. While Sailor Mercury's civilian name 'Mizuno Ami', the word "mizu" in "Mizuno" literally means water in Japanese, and Sailor Mercury's element is water, because the planet Mercury is literally called the "Water star" in Chinese, Japanese and Korean. Same with Sailor Mars, her name 'Hino Rei' the word "hi" in "Hino" literally means fire in japanese and Mars element is fire while the planet Mars is called the "fire star", and so on, so all their names are very literal to their planetary names and elements, at least that's how it is for the inner senshis and Sailor Chibi Moon, I'm not sure about the outer senshis though.