In addition to the Galaxy Expedition Team you're a part of in the game, you'll also encounter members of the Diamond Clan and Pearl Clan as you travel throughout Hisui. The people of the Diamond Clan often speak of the importance of cherishing the present and living in the moment with one’s allies. On the other hand, members of the Pearl Clan frequently advocate the importance of valuing the vast, spacious land shared with others.
Although the Diamond Clan and Pearl Clan disagree on many of their beliefs, they seem to nevertheless share many similarities. Both clans don clothing designed to resemble certain Pokémon, and both pay respects to special Pokémon they call lords and ladies—or collectively, noble Pokémon. Moreover, both clans have wardens who serve these special Pokémon.
In fact, we've already met two of these wardens in previous updates. Lian, who serves as Warden in the Obsidian Fieldlands for Kleavor - the new Hisuian evolution of Scyther revealed a few months ago - is a member of the Pearl Clan. While Arezu, who is pretty evidently related to Team Galactic's Mars, is a member of the Diamond Clan and serves as Warden for a 'certain Lady Pokémon' that has yet to be announced.
During the trailer we also get a chance to meet the two leaders of the clans, Adaman and Iridia. Both curiously refer to a certain entity as 'Almighty Sinnoh', marking the first use of what will become the Hisui Region's name following this game's events. It's unclear what they might be referring to, but it seems pretty likely it's going to have something to do with Arceus...
Adaman serves as the leader of the Diamond Clan and has Leafeon as his partner Pokémon.
This daring young man hates seeing time go to waste and likes to rush forward without worrying too much about particulars. This way of thinking puts him at odds with Irida, who leads the Pearl Clan, so the two are frequently seen fighting.
Irida serves as the leader of the Pearl Clan, and her partner Pokémon is Glaceon.
As a leader, she feels it is important to have the courage to face the vast Hisui region without quailing before it. Though she is suspicious of you when you first meet, she will come to trust you thanks to the help you provide in quelling the noble Pokémon.
As well as these two clans, two characters of the Ginkgo Guild have also been introduced.
One last character also revealed in today's update is Iscan, who lives by the sea and cares for a special Basculegion that makes its home in the area. He can be a bit easy to frighten and isn’t too fond of Ghost-type Pokémon. He and Mai, who also wear Diamond Clan outfits, both seem to serve as Wardens for the Wyrdeer and Basculegion you'll be able to ride on in-game.
Finally, some bonuses have been announced for players who have Pokémon Brilliant Diamond or Shining Pearl saves on their console.
Once you have completed the main game and returned to Jubilife Village, you'll be able to accept a mission to find and catch Darkrai, much like the Shaymin mission announced a short while ago for having Pokémon Sword and Shield save data.
Prior to that, however, you'll also be able to claim the Modern Team Galactic outfit set by speaking to the clothier after joining the Galaxy Expedition Team (about an hour in to the game). These join the Shaymin Kimono set you can claim for having Sword or Shield, Pikachu and Eevee themed masks for owning Pokémon Let's Go Pikachu or Let's Go Eevee and the Hisuian Growlithe Kimono set and Baneful Fox Mask available over online Mystery Gift from launch until the 9th May 2022.