This is the 7408th most frequent Japanese word.
佑介
"佑介" is a Japanese male given name, typically read as "Yūsuke," meaning "assist/protect" (佑) and "help/mediate" (介).
In this sentence, '佑介' serves as the proper noun representing an individual's name, used as the subject of the sentence.
佑介は私の親友です。
Yusuke is my best friend.
Here, '佑介' refers to the sender of the email, indicating interaction with a person named Yusuke.
昨日、佑介からメールが届きました。
Yesterday, I received an email from Yusuke.
In this case, '佑介' is being discussed as an example of a common Japanese name, demonstrating a more general reference.