Who is bad guy in this story ?

[234432432342]

Sekiro ?
Owl ?
Isshin ?
Robert ?

[Shichiya]

Genichiro and Owl I believe

[OCTDUMPUS]

Anyone that stand in your way shall perish.

[Yian Yan]

Either strictly anyone you fight or, if you're examining motives: probably only really Owl, the Interior Ministry gang, and the bandits.

Sekiro is just a shinobi working to serve (and save) his lord. He can become an undisputable bad guy if you make him mindlessly follow his Iron Code.

Genichiro is the main antagonist but he really just wants to protect his lands and his people by any means necessary. He's just, sadly, also really dumb and doesn't consider the consequences of what he's seeking.

Robert is, I'm pretty sure, just a sick kid whose dad wants to save him by the miraculous powers of the rejuvenating waters.

Isshin led a rebellion to free his people and now is really just there as an old man having fun (admittedly largely by killing) while protecting his lands and his ideals.

Owl is one of the few viciously self serving individuals who is after immortality as a means of world domination and will violently betray (almost if not) literally anyone who gets in his way. Including his own (adopted) son. Multiple times.

The Interior Ministry is the outside invading force whose motive is shown as really just exploiting Ashina's current weakness to conquer.

And the bandits are, well, bandits.

..

Oh, and the Senpou Temple gang. They're all kinds of just awful.

[Pnume]

Owl take the take.

Genichiro is misguided but Owl is doing what he is doing for purely selfish reasons.

[SmallGespenst]

Sekiro doesn't really buy into absolute good/evil, the "antagonist" is Genichiro, because he acts as the main barrier preventing wolf from rescuing kuro/ achieving immortal severance. pretty much all of the "evil" characters are just acting in self-interest, not some kind of absolute evil conspiracy.
in short: there is no "bad guy" just obstacles

[Ashtrails]

Hard to tell, since it's really a matter of perspective:
Almost everyone you meet (by which I mean 'kill') just want to save their home from invaders.
As early as when you kill Gyobu, you should realise that you, personally, invite death and destruction to Ashina by killing its finest and most reliable lines of defense.
The invaders want to unify Japan so the endless cycle of war finally stops, indiviudal territorial preference be damned.
Owl wants to cash in his well deserved reward after a lifetime of servitude in a way a lifetime of war, death and shinobi lifestyle taught him.
The sword saint... well, he wants to go out with the biggest fight of his life and preserve his home as a secondary concern.

And he and Kuro also kiiinda identify the true evil force of the game in my opinion: the corruption of immortality and the ambition and greed that comes with it, the shura and all that.
So yeah, guess the bad guy here is not a person, but more of a spiritual concept taking form? : D

[二锅头男孩]

Why Robert LOL??? It must be the man in red suits with a pair of swords!
I am in Asia civilization culture, knowing a little bit of Japanese traditional history. Genichiro is a good guy but he became too Superstitious in the power of the dragon. Sekiro and Genichiro belong to a same camp but Sekiro's master refused to abuse dargon's power because of the plague caused by it.
The troop in red clothes in the middle and end of this game in Ashina derives from the Ace army of Tokugawa Ieyasu, who is a Great General(this kind of appellation may be familiar to a dictator, but not in the same meaning specifically such as the prime minister of England ) in ancient Japan. You can look at his autobiography in WIKI.

[往事随风]

Robert

[dande48]

IMO, just about everyone is the bad guy, except Buddha, the Divine Dragon and Kuro. And Sekiro, if you don't go "Shura".

You're caught in the middle of a civil war. The Ashina clan lost their land. The general Isshin rebelled and took it back. The Imperial government doesn't like that, so they sent their armies to quash the rebellion and reclaim those lands. The only way Ashina can win, is if they have a strong edge. So Genichiro captures the divine heir, and wants to use the divine heir's powers to make his army immortal. Kuro won't, because that power corrupts people and makes people sick. So Genichiro goes out to find the only blade that can harm Kuro, to force him.

Owl is a bandit, who placed Sekiro as Kuro's guardian, in hopes of later claiming the same immortality.

So it's like with any war... who the "good guy" is depends who's asking. Sekiro is only on Kuro's side... and everyone wants Kuro for his power. Kuro wants his immortal powers to go away. Those immortal powers come from the Divine Dragon, who has been wounded. So the main quest of Kuro/Sekiro is getting those powers out of the mortal realm, and back to the Divine Dragon. But this leaves Ashina pretty screwed.