The particle 'WA' is a topic marker, akin to saying "as for (word preceding 'WA'); the particle 'wo' indicates the word before it is a direct object of a verb. Mamoru means 'to protect' or 'to defend'.
君"Kimi" is a way of saying "you", not "I" or "me".
君を守る "kimi WO mamoru" would be "(I) protect you" and
君は守る "kimi WA mamoru" would be "you protect (something)".
This is from a Japanese pop song a few years back.
Asana Mamoru is 171 cm.
Mamoru Shiragami was born in 1944.
Mamoru Sasaki was born in 1936.
Mamoru Sasaki died in 2006.
Mamoru Fujieda was born in 1955.
Mamoru Uchida was born in 1900.
Mamoru Uchida died in 1982.
Mamoru Kuroiwa was born in 1962.
Mamoru Imura was born in 1948.
Mamoru Kanbe was born in 1962.
Mamoru Sato was born in 1937.
if im right, mamoru (tuxedo mask) is a college student. usagi is around 14 ( i dont know the exact age of tuxedo mask)