Surprise! To no one. Like Bloodborne and the Souls series Sekiro: Shadows Die Twice has multiple endings. Four to be precise. There’s the easy ending, the real ending, the true ending and the other ending that adds some extra lore. Those aren’t the real names. There’s the Shura Ending, the Purification Ending, the Immortal Severance Ending, and the convoluted Return Ending. Each has a few steps you need to follow to unlock it. Obviously, there are spoilers ahead.
This is the easiest ending by far. Just play through the game naturally and kill every boss you come across your father atop Ashina Castle. This means Kuro will send you on a quest to complete a fragrance which entails you collecting the mortal blade (folding screen monkeys), a flower (Corrupted Monk), and a stone (Guardian Ape). Once you have these items head to the castle to find it under siege. Fight your way to the top of the castle and you’ll be confronted by a choice from your father. Choose to “Obey the Iron Code, Forsake Kuro”. This will begin the Shura ending and you’ll have to fight Emma and Isshin. This means you’ll miss out on a huge area and Sekiro’s best boss battles. After beating Isshin you’ll have achieved the Shura ending.