I'm going to have to mention blade dancing here, because it's honestly the silliest one I've got at first glance, but the Mordena take it very seriously.
The Blades are the Mordena's homegrown space fighters, each piloted by an Afterlife Intelligence, the soul of a dead Mordena who has elected to return as a fighter. The Dancers are their pilots, or technically more the gunner since the Blades fly themselves. In fact, Dancers are equipped with telekinetic gloves and boots so they can also operate outside the Blade, although of course there are safety concerns and plenty of training involved. (Most important: Deactivate the telekinetics when going through Portals, then reactivate on the other side).
In blade dancing, two squadrons face off and attempt to achieve a specific goal while blocking the opposing squadron from doing so. The objective can vary, the official league has some sort of sportsball rules set up as default but this can be changed to anything so long as both squadrons plus the host/judges agree, so games can range from violent races to semi-simulated combat to hunting down the dragon birds plentiful across the planet. Points are lost for killing or severely injuring opponents, even more for a Blade than a Dancer (resurrections take resources which are must better spent on actual combat than play, after all) but temporarily incapacitating members of the other team is often encouraged. It's nothing personal, and good practice for facing the Confederation or the Order, who never pull their punches.
Afterward both teams co-host a social with their fans, lots of revelry and teasing and no hard feelings. The Mordena are a rowdy bunch that often appear callous and uncaring to outsiders but in truth they're led by a necromancer so death is less of a concern than living to the fullest.
Tell me about a musical instrument and the culture it represents.
