Jump Force came out this past February and introduced a few new characters into the mix: two of which (Kane, Galena) were boss characters. Much to the chagrin of the community, however, Bandai Namco did not make them playable, even as unlocks...until now.
Due "the week of July 22" (so any day now), Jump Force is getting a huge free update that adds Kane and Galena as playable fighters, as well as a type D sword style, and online raid boss battles. As Bandai Namco notes, raid boss battles are "limited time events" that allow you to partner up with clan members, so long as you have event tickets from the in-game shop. In turn you'll get event points, which you can turn in for extra rewards.
So yeah, if you haven't booted up Jump Force in a while, you could potentially recruit some of your friends to clan up and try out these weekly events.
1.10 and 1.11 patch notes [Bandai Namco]