"Older Brother"\"Senior Student"

"Older brother" (or more commonly "senior student") is a term used in Puroresu to signify that two people have been trained by the same person. The term "older sister" is used among Geisha for the same reason.

Age does not play a role in determining who is senior, as for example Naomichi Marufuji was born in September 1979, but he is the older brother\senior student of the older in years Kotaro Suzuki who was born in 1978, because he was trained before him by Mitsuharu Misawa and he debuted before Suzuki, Marufuji is therefore the elder student.

KENTA & Go Shiozaki are another example, as both were trained by Kenta Kobashi. The bond between KENTA and Kobashi is absolute, with KENTA still going to Kobashi for advice and mentorship, and Kobashi supporting KENTA no matter what he does and where he goes. Kenta Kobashi had also used to address Mitsuharu Misawa as, "Oniisan" ("Older Brother"), which is what Kotaro Suzuki calls Naomichi Marufuji. 

The other term for "older brother" is used between Kenoh and Kaito Kiyomiya. Kiyomiya is Noah born, whereas Kenoh came from Michinoku Pro. Their relationship is likened to brothers, not only because they were in a unit with Takashi Sugiura together (who bought them both into the heavyweight league), but because there is this bond between them (although they are often at each other), which is like brothers with Kenoh swinging between hatred, jealousy and concern for the much younger Kiyomiya with the pressure the company has placed on him and what will happen to him in the future, and Kiyomiya (despite everything) looking up to Kenoh, (despite the fact he hates him), and also adopting his blonde hair and similar hairstyle. Kenoh is also the only person who Kiyomiya isn't scared to be (slightly) rude to. Their short lived tag team strengthened these bonds, as Kenoh was often seen giving advice to Kiyomiya, and for once...smiling.
Behind the scenes there is a bond between them, as they often practice together at the dojo (Kenoh says he doesn't like training with lots of people, but seems to tolerate Kiyomiya) and the touching moment when Kiyomiya almost fainted due to a neck injury at the Misawa Memorial in 2018, and Kenoh reached out to steady him. 

"The Mighty Don't Kneel" (Shane Haste and Mikey Nicholls) refer to Hitoshi Kumano as "little brother".