This is the 9593rd most frequent Japanese word.
美津子
"美津子" (Mitsuko) is a Japanese female given name meaning "child of beauty and harmony."
Here, '美津子' (Mitsuko) is used as a proper noun indicating a person's given name, with 'さん' expressing politeness.
美津子さんは親切な人です。
Ms. Mitsuko is a kind person.
In this sentence, '美津子' is used as a proper noun stating the name of someone's acquaintance or friend.
昨日、美津子と映画を見ました。
Yesterday, I watched a movie with Mitsuko.
This sentence uses '美津子' as a possessive indicating that the diary belongs to Mitsuko.