I have info on Sword and Shield. There's a lot of rumors going around right now, so this will be one in a sea of many, and probably won't be believed, but (and I know this is one of those "leak" cliches) I got my information from a close friend/source who has never once told me wrong about upcoming news/info.
Main Legendaries:
Sword's Legendary is an offensive Wolf Pokemon. He is a large Wolf which an ability that boost his attack stat when he knocks out a Pokemon. His name is "Howla"
Pokemon Shield's Legendary is a Defensive Lion Pokemon. Everytime he knocks out another Pokemon his defense stat raises. His name is "Ligard" (basically the legends are opposite of each other and promote different play styles to appeal to different players.)
It is heavily implied throughout the early story that 3 Pokemon were placed in power in the Galar region, and there is a story told that one of the Pokemon was afraid of it's power and destroying the region so the Pokemon ran away and concealed it's power. This Pokemon is later revealed to be Zygarde by Dexio and Sina. The evil team "Team Tripsy" wants to obtain the power of Howla and Ligard to summon Zygarde to use his full power to take over the Galar region. The team leader always wears a mask which is supposed to imply that it is an important character, a character you might even be close to and related to (which it is). This may sound a bit out there, but yes this is apart of the actual story: your Father is the leader of Team Tripsy. He plans to use the legendary Pokemon to take over the Galar region and plunge it into darkness.
Fast forwarding through the story a bit here, you and your friend/rival reach the location of the "Howling Horn" and "Roaring Horn". They summon Howla and Ligard, however you are too late. You realize the Howling Horn (or Roaring Horn depending on version) was missing, and as your father calls the legendary Pokemon Ligard (once again depending on version) Howla jumps down to battle at your side. 1/2