This phrase is common in many anime. You will especially here it when a character is refering to someone who is important to them.
The following situations are common:
-company (people that you are in the company of)
-colleague(s)
-associate(s)
-comrade(s)
-mate(s)
-circle of friends
-a partner
These words mean "brother". Three different suffixes are always attached.
oniichan (お兄ちゃん) - This is used in casual and informal situations as well as affectionate settings.
oniisan (お兄さん) and oniisama - These are more honorific and used in more formal settings that denote respect.
In some animes the "o" is left out and just niisan is used. Usually by a younger sibling when talking to an older brother.
The suffix -sama is usually used to define great respect for someone who is much older and wiser or of much greater social rank. This suffix can be used for either male or females.
The Japanese word shounen is used to refer to young males. It is often used to categorize an anime series when most of the characters are young males.
Pronunciation: ‘sho-nehn’