Sumo's family unit is the stable.
A wrestler's life is defined by his heya (stable) to such an extent that "family" is no mere analogy.
While they may not be related by blood, a stablemaster and his wrestlers live, eat and sleep in the same building and spend more time together than many actual families do.
Stables aren't the only grouping in sumo however.
All heya belong to one of five extant ichimon (clans).
Those are Nishonoseki, Dewanoumi, Tokitsukaze, Takasago and Isegahama.
Each clan takes the name of its leading stable.
In the past ichimon members had a tighter relationship, but in modern times the main function of the clans is to serve as quasi-political groupings.
The clans nominate candidates for the ten positions that are available on the board each election cycle. The vote normally takes place in January or February of even-numbered years.
Voting for members of the Japan Sumo Association's board of directors is normally along ichimon lines.
As with any kind of politics, however, there is often intrigue and subterfuge, resulting in splits and new coalitions.
In the past there have been non-aligned heya, or lose coalitions that weren't formal ichimon, but in 2018 the JSA ruled that all stables had to belong to one of the current clans.
The 46 stables in existence aren't equally divided among the ichimon.
Nishonoseki has the most heya with 15 but Dewanoumi has the most affiliated oyakata (elders) with 35.
The current JSA chairman, Hakkaku, is a member of Takasago Ichimon.
The various clans hold joint practices prior to tournaments. These tend to have some of the most intense training sessions, and since many of the top-ranked wrestlers face each other, are a good indicator of health and form heading into the bimonthly meets.