Okay, the plot is from Okita Mitsuba arc, in the manga it is like a minor arc but a very important one since it explained the history of the three important Shinsengumi officers. I really like Hijikata in the manga, so I am happy they chose this arc since he didn't have too much screen time in the live action lol. You can just watch this one without watching the live action, the storylines are not related. It focused on Sougo and Hijikata with Gintoki on the background. Gintoki is still as awesome as ever even only as a sidekick, don't worry. But Shinpachi and Kagura didn't appear here. Just like the live action, this drama literally follow the manga and didn't change any of the plot so it is very enjoyable for the fans. It used the same style and music from the live action so it didn't feel like two different Gintama. You can just watch it alone or complete it with the live action. Nicely done, recommended.