As any fan of the Soulsborne series could tell you, the games are not easy to understand. Whether it be the mechanics of the game, or the often seemingly incomprehensible lore being the loose stories attached to the games. From Software, and specifically director Hidetaka Miyazaki, loves to confound players. Esoteric ideas such as cycles of time and knowledge beyond human comprehension are as common as the "YOU DIED" screen that haunts every playet to their grave, but Sekiro is a precedent for the series in a number of ways, including a gameplay overhaul. However, we only have a few snippets of information on that regard, so I cannot comment too heavily on the nature of those changes.
One readily evident change is the setting. Soulsborne games have been defined by their unique take on European-inspired Dark Fantasy, with little import of the culture of their country of origin, Japan. Whether it be the sprawling Gothic cities such as Yharnam to the foreboding castles of Boletaria, the influence of European architecture and culture were self-evident. Even down to the voice acting, even in the Japanese releases of these games, the default languages NPC's will speak in is English. Sekiro seemingly is departing from this tradition. While I do not know if a Dual-Audio setting will be available in the North American release of this game, I would prefer to listen to the Japanese Characters of Sekiro to speak in the native tongue of the land. Bonus points if they speak in antiquated Japanese.
Beyond just the setting and voice acting, we can analyze one more thing about the game that is self-evident; the title, Sekiro, is a combination of the characters (seki), meaning "one half of a pair," and (roh), meaning "wolf." I take this to mean "A pair of wolves," though Japanese is hard to correlate to English. This is, I believe, in reference to the other Samurai that you see cut off the currently nameless protagonist's arm, and the constant struggle between these two characters will likely form the crux of this game's plot. Upon consulting with a native Japanese speaker, they confirmed my theory though also added that since it is a new world, it could mean "half-wolf," or werewolf. I think this is unlikely, unless From Software either wants to throw a curveball, or means it in the same sense that Geralt from The Witcher series is called "Grey Wolf." This is corroborated by the tagline given by From Software, themselves, on the press release of Sekiro, "Defy Sengoku as the One-Armed Wolf."
This press release also confirms the time period as the "closing years of the Sengoku period." This was the warring-states period that took place from roughly 1476 to 1568, so Sekiro takes place in the early-middle 16th Century.
The "Shadows Die Twice" tagline is a little more confusing without context, though it seems as if the "Shadows" are a translation of the trend in Japanese to refer to ninja as "Shadows." The "Die Twice" elements seems to be the ability for the protagonist to either respawn, or just revive, though how this mechanic will be implemented is yet to be entirely seen.
While From Software has stated that this game will be in form with the beloved confusing nature of story-telling they have become famous for, I think they are taking a cue from a game that they, in turn, inspired. 2017's Nioh, was a Soulsborne-inspired game that took a more traditional route to story-telling, with a non-customizable protagonist with his own personality and look. Sekiro seems to be taking the same route, though how much Nioh has inspired it remains to be seen.
Sekiro: Shadows Die Twice is one of my most anticipated games of the coming year, and I cannot wait to get more information on this title.