This is one of the two endings you will reach without going out of the path in Sekiro. After defeating both the Corrupted Monk and Guardian Ape, and collecting the respective items requested by Kuro, Owl will be waiting at the top of Ashina Castle Tower. You will have to make a decision which will impact what ending you get. For this ending, you must choose "Obey the Iron Code, forsake Kuro".

After making the decision, you will end up fighting two bosses (See  Isshin Ashina), after which you will reach this ending. Do note that this ending locks you out from the other 3 endings, which share the opposite decision when asked by Owl (serving Kuro).