The first two seasons contain minimal amounts of actual blood. With Season 3 (Alicization), however, this season projects a darker narrative and contains a more blood and is more violent than the other seasons.
Alicization is much darker than seasons 1 and 2, and it shows in its violence, being much more violent, explicit and graphic.
Season 3 is more graphic and show actual blood and not pixels like Season 1 and 2
In the Blu-ray version, the shadow are never showing, but the eye are visible blows up, and chopping arms with a lots of sprays bloods in Season 3.
Seasons 1 and 2 use pixelated pink-red blood, while seasons 3 and 4 use graphic blood.
Seasons 1 & 2 aren't too bad; what would be expected from sword and sorcery and more PG-rating. Seasons 3 & 4 are EXCESSIVELY AND GRATUITOUSLY bloody and gory.
Seasons 3 & 4 should probably be rated TV-MA for nudity and gore.
In season 3/alicization and season 4/war of underworld there is a lot of blood if I was going rate the season 3 second half and season 4 I would rate it severe.and if I was going to compare it's violence and gore I would say it has a much blood as in Akame ga kill and some episodes have as much blood as in attack on titan
Sword Art Online takes place in the future within a virtual reality video game. There is no blood shown when people are stabbed or slashed at, the only thing that shows up is some red pixels that represent where a player was cut, or fatally injured. Therefore, one should keep in mind that the violent content here is virtual unless stated otherwise.
The storyline for episodes 1-14 goes as follows: 10,000 people are trapped in a virtual reality video game, and the only way they can escape is by completing the game, because if they die in-game, they will die in real life. It's a rather intense premise and it is said that approximately 4000 players die as a result.
There are near-constant battle sequences between monsters and players. These scenes can be fairly intense.
A few suicides (they jump off a ledge and then burst into pixels as they hit the ground).
Episodes 15-25 follow a similar premise as the first 14, but players do not actually die if they do in-game.
A boy's hand is chopped off with no blood (in the game). He then takes his other hand and lunges it through another man. He later has his hand regenerated (since it's in a game).