Dragon Ball Z: Kakarot players will be able to access new content on 28 April 2020 when they get to encounter Beerus and get training from Whis. One interesting twist is that you can use the newfound power on weaker enemies, like Raditz.
Dragon Ball Z: Kakarot season pass consists of two boss battle episodes and one additional scenario. In the words of Ryosuke Hara, the boss battle episodes' sizes will be roughly the same as "a few Sub Stories combined" while the additional scenario will be about the size of a single saga.
In the case of Beerus and Whis' arrival, it is the former, so the content is not that chunky but it will give players an opportunity to gain new powers and a new boss that they can fight at any given time.
The boss is Beerus, as you probably guessed by now, and players can go fight him whenever they want, without having to complete the story campaign, if they are confident enough. Furthermore, the new training they get will allow them to achieve the SSG form, giving them a tremendous power boost.
Since there are no content completion or time restrictions, this means that players will be able to gain power and then start with the story campaign. The announcement confirmed this possibility, stating that it would take a single blow to wreck Raditz, should a player go down this lane.
One interesting detail is that the story will not follow the one from the Battle of the Gods movie and will focus on battle gameplay in an original setting. That also explains why both Goku and Vegeta reached SSG in the picture above.
There is a second boss battle episode in development and there are no spoilers just yet but Hara noted it would be a good idea to start levelling and upgrading the characters as much as a player can.