The name Old Friend in Chinese / Japanese...

親友 is the Japanese way to say “best friend.”

The first character can mean “relative” or sometimes “parents.” The second character means “friend.” Think about the close relationship that Japanese people have with their parents and relatives, and this starts to mean “close friends.”

Some Japanese-English dictionaries also translate this as “bosom friend,” “old friend,” “intimate friend,” “buddy,” “crony” or “chum.”

Note that in Chinese, this means “relatives and friends.” It's a good meaning in Chinese, but it's not quite the same as “best friends.”

朋 is a simple way to say friend, companion, comrade, or pal in Chinese, Japanese Kanji, or old Korean Hanja.

朋 is a very short form, so a longer two-character word for friendship might be better.

Note: In Japanese, this can also be the female given name, Yukari.

仁恕 is a word in Chinese and Japanese that means something like benevolence with magnanimity or kindness with a forgiving nature.

If this describes you, then you are the type of person that I would like to call my friend.

This may not be the most common word in daily use, but it's old enough that it transcended cultures from China to Japan in the 5th century when Japan lacked a written language and absorbed Chinese characters and words into their language.
Note: 仁恕 is not commonly used in Korean.