Notes

Paintings and drawings in the outro: according to one story a woman called Ymir Fritz made a deal with the devil who gave her powers, so Ymir became the very first titan in order to save her nation in the war. According to the other story she found "the source of all organic material" and thus became a titan. Becoming a shapeshifter will kill you after 13 years, so when the 13 years passed, Ymir Fritz's power created 9 powerfull titans, one of them was the holder of Ymir's power, the Founding Titan, who can conrol "normal" titan (=not shapeshifters) and manipulate people's memories.If you want more then the decendants of Ymir Firtz were the Eldians, who defeated the Marley Kingdom. A group of Marleyan survivors made a revolution and somehow took over 7 titans' power from the 9. A part of the Eldians led by king Fritz (who was the holder of Ymir Fritz's powers) escaped to an island called Paradis, wehre he built the giant titans of his nation into the walls. This is where the current story plays. The others lived under Marleyan control in ghettos. If a titan shapeshifter dies then a random Eldian will inherit its abilities. To prevent this, the Marley kingdom always names a person of them who eats the shapeshifter before it dies. Every shapeshifter can live only for 13 years after receiving the titan power. So by eating each other they can hold the power with them and not lose it. Also the Marleyans made a serum from the body of the titans. If someone is injected with the serum, then he will turn into a "normal" titan for the rest of his life, can't control his doings, and it is like a nightmare for him.ime by the time the Marleyans bring Eldians to Paradis, inject them the serum, so the Eldians transform into a titan forever and they are left at Paradis in order to eat the Eldians who escaped there. This is the origin of titans.Grisha Yeager was born into an Eldian ghetto in the Marley kingdom. Marleyan soldiers killed his sister, so Grisha joined the Eldian revolution and became its leader. An Eldian who is known as "Owl" sends a decendant of Ymir Fritz called Dina Fritz to the revolution in secret. Grisha married Dina and they had a son called Zeke. Marleyans decided they will give titan power to an Eldian kid, so the parents are free to give their kids to the army. Grisha's plan was to give Zeke to the army, Zeke will become a great soldier and thus he gets a titan power and becomes a shapeshifter, and then he will destroy the Marley kingdom from the inside. However Zeke betrayed all of the Eldians. They were brought to Paradis, where the murderer of Grisha's sister turned everybody into a titan by the serum. Dina was turned into the smiling titan, which ate Eren's mother, so Grisha's 1st wife ate the 2nd wife. When he wanted to turn Grisha into titan, a soldier disclosed that he is "Owl". He is a titan shapeshifter, he turned into a titan and killed everybody except Grisha. He told Grisha everything. Owl was called Eren Kruger. He made Grisha to eat him and thus Grisha got the titan's ability, the titan who is called Attack Titan. Then Grisha went inside the walls, started a life, and at a point he visited the royal family, turned into titan and devoured the holder of Ymir Fritz's power. With this he wanted to get the Founding Titan's ability, free the titans from the wall, and control then to destroy the Marley Kingsom. However only royal family can control the titans. Grisha went home, and to hide the Founding Titan's power from the king and his men, he injected Eren with the serum, Eren turned into a titan and devoured Grisha. Eren didn't remember this. So Eren is the holder of the powers of the Attack Titan and the Founding Titan also called the Coordinator.
And the beast titan is Zeke Yeager, the brother of Eren!King Fritz who escaped to Paradis many years before the story, erased the memory of all of his people, so the king was the only one to remember the true history, and he said to everybody that they are the last of humanity. Escapees arrived to Paradis, the Ackerman family. They became close friends with king Fritz, however they are not Eldians, so Fritz couldn't erase their memories and after a period of time he looked at them as enemies and ordered them to be executed. Only a few Ackerman survived and lived in isolation in secret. The king was eaten by his decendants after 13 years, so the decendant inherited his powers and the knowledge of history. Then he was eaten by his decendant etc. etc. this is how the Founding Titan's power stayed in the royal family.
One day a few years before the current story, a serial killer called Kenny the Ripper, wanted to kill the king to revenge the Ackermans. Kenny Ackerman is the uncle and mentor of Levi Ackerman. Kenny failed, but he was spared and became the loyal guard and killing machine of the king, and a leader of a Military Police squad. The current king is a Fritz, however he is only a puppet of the real king, Rod Reiss, who origins from the Fritz family too and Kenny is his servant. Rod commands Kenny and his group to kill inventors, coz he wants his people to not be able to use advanced technology, so he can restrain them easier. Rod discovered that Eren owns the Founding Titan, so due to his orders, they built new 3DMG which is built against the Survey Corps. Kenny is ordered to kidnap Eren and Krista, and slaughter the whole Survey Corps. Krista is the secret bastard daughter of Rod Reiss, originally called Histora Reiss.Meanwhile, the current story of the anime, Connie discovers that his family and everybody of his village, are turned into titans somehow. Night comes, Eren and his friends are cornered by titans, titans become active at night due to the Beast Titan. They can't fight them all, so Ymir (the brown skinned boyish girl usually seen with Krista) reveals that she is a shapeshifter and turns into a titan to save Krista and the others. Reiner and Bert discover that Ymir is the Dancing Titan, who devoured their friend a few years ago. Ymir is a small titan, but very fast, can speak in his titan form, and move in and out of her titan body even during fights. They escape and make it to the wall to fill the holes. There suddenly Reiner and Bert reveal that they are the Armored and the Colossal Titan! Mikasa tries to kill Reiner, but fails. Eren aka Attack Titan vs Reiner aka Armored Titan, everybody vs Bert aka Colossal Titan. Eren due to the training from Annie, is able to defeat Reiner, but Bert jumps down from the wall in his colossal size and KO Eren. They take Eren and Krista, run away, but Ymir chases them. Reiner, Bert and Ymir tell the truth to Eren and Krista. Ymir is an Eldian who was turned into a titan. Wandering, she found Reiner and co., and devoured their shapesifter friend, so she got his power and became a shapeshifter. It is against the laws of Marley Kindom, so Reiner and Bert have to bring Ymir home to be punished. Reiner, Bert and Annie got a mission to break the wall and let the titans in. The mission ended, they didn't find the way home, so stayed there and joined the Survey Corps in order to find the way to home. The Beast Titan knows the route, so they need to find him in order to go home. They bring home Ymir, coz what I said before, Eren, coz somehow he is a shapeshifter, and Krista,coz he is the daughter of the king.Meanwhile the Survey Corps are outside the walls to find them. They arrived, but are sorrounded by titans. Survey Corps vs Reiner+Bert vs titans. The Smiling Titan, which ate Eren's mother, arrives. Eren wants to transform and kill it, but he is too weak to transform. Hannes tries to save him, but he is devoured by the Smiling Titan. The Smiling Titan reaches for Eren, Eren hits it palm with great anger, and then the normal titans attack and devour the Smiling Titan. Reiner and Bert discovers that Eren is the Coordinator, but they need to escape with Ymir leaving Krista and Eren behind. Erwin loses an arm. The Survey Corps lost a lot of men, they go home, where Kenny kidnaps Eren and Krista, and starts to assassinate them. Erwin is about to be punished for treason, but he cooperates with Pixis and commander Zackly who is the head of all the army, and they make a coup, taking over power in the walls.
Meanwhile Rod Reiss tells Eren and Krista, that he wants Krista to be injected by the titan serum and devour Eren, so the Founding Titan's powers will return to the royal family. Krista is against it, and Eren can't do anything, coz he is shackled. Rod tells them that he ordered Krista's mother to be executed by Kenny, and that only the royal family can control the titans with the Founding Titan's ability. Kenny hears everything and becomes angry, coz it seems he wanted to gain this power in secret, Rod knew it and made a fool of Kenny. Then Rod insults his dead brother, Uri Reiss, who was the one who became friends with Kenny and hired him as his guard. Also Rod wants Krista to eat Eren, coz he is afraid to do this. Kenny doesn't like what he hears and sees, so he pushes his sword down Rod's throat leaving him to slowly bleed to death, then he frees Eren and cuts him in order to be able to turn into titan form. Rod in his anger injects himself with the serum and turns into an abnormal titan bigger than the Colossal. Since they are in a basement, it would make the ceiling fall, but Eren finds a flask with text "ARMOR", he drinks it and gains temporary powers with what he hardens the ceiling and walls. In this time Levi and the others are fighting Kenny's men in the basement.Rod as an abnormal titan is wandering above. Levi finds Kenny who suffered fatal injuries and is can't decide: die or inject himself with the serum and turn into a titan. He decides to die and gives the serum to Levi.
They kill Rod and lie to everybody that it was Krista's doing. Krista becomes a hero for the people, they reveal that she is the daughter of the king, so Krista is crowned as queen. Meanwhile Reiner and Bert found Zeke aka Beast Titan. They asked him to save Annie, but Zeke said no. Reiner attacked Zeke, but was easily beaten. Zeke told Reiner not to go against him again, coz he can take away the Armored Titan as easily from him as easily he got it. It makes Reiner to shut up and follow Zeke's orders. Also Zeke hints that Reiner is only a soldier, but Bert is a leader. Zeke has a plan to crush Paradis.
Under Krista's reign tecnology advanced a lot. The whole Survey Corps with fresh recruits go to fill the holes in the wall and reach Eren's basement. When they reach the wall they spot Zeke. Zeke is standing with a lot of titans around the wall preventing them to pass. Zeke starts to throws rock at the speed and power of canons nonstop killing a lot of the Survey Corps and their horses. Reiner was hiding inside the walls and turns into titan form to kill them. They made a new weapon only for Reiner called "Thunder Spear", these are spear-like projectiles which are able to cut through Reiner's body, and then blow up in an explosion. They blow away Reiner's head who is about to die. Meanwhile Zeke throws human Bert into the air. Their plan was that while the humans fight Reiner, Zeke throws Bert into the air, Bert turns into full size Colossal Titan and jumps down killing everybody. However he notices that Reiner is at the verge of death and is not able to protect himself from Bert's impact, so Bert cancels the plan. We know that Reiner replaced his organs before the explosion so he survived. Reiner vs Mikasa and the others, Bert vs Eren+Armin who has a plan to kill Bert, and Erwin starts a suicide attack with the fresh recruits on Zeke in order to distract his attention. Erwin's plan is to be the bait and die to Zeke, while Levi jumps from the wall, through the titans killing all of them and making his way to Zeke and kill him.
Zeke kills everybody, but then Levi reaches him. Flashback: Reiner tells Zeke to be very careful against Levi, coz he is a monster. Flashback ends. Levi slices Zeke's titan body, cuts him out of the nape, and captures him. Mikasa and co. can't blow Reiner's head again, coz he protects himself better now. Mikasa shoots a thunder spear into Reiner's mouth which blows Reiner away from the nape, and he is captured. Armins plan: Eren pretends that he can't find against Bert. To make Bert believe it, Armin jumps onto Bert's hot body to save Eren at the cost of his life. Armin burns to black. Bert makes it to the lying Eren, discovers that it is only the hardend titan body what Eren left behind, but it is too late. The real Eren is already behind Bert, cuts him out of the nape and captures him.An abnormal talking titan saves Zeke from Levi. They make it inside the walls and save Reiner. They don't have time to save Bert, so they leave.
The survivors gather: Eren, Mikasa, Levi, Connie, Hange, badly inujured Jean and Sasha and dying Armin. Levi has the serum from Kenny. The plan was to capture one of Reiner, Bert and Zeke. Give the serum to a fatally injured member of the Survey Corps thus turn him/her into a titan, and make him/her to devour the captured enemy, and Levi is the only one who has the right to decide who he wants to save. Eren is happy they can save Armin like that, but then a survivor recruit arrives with the dying Erwin. Levi decides to save Erwin instead of Armin, they go away while Levi injects the serum. To everybody's surprise Levi gave the serum to Armin. Armin turns into a titan and devours Bert inheriting the Colossal Titan's powers.
Then they make it to the basement where they learn the origin of titans from Grisha's books.