(Note: his full story can be found in AO3 )
"goodnight, you little glitch." - Error to Ink, before 'killing' him.
Ink finally had enough of Error destroying everything he loved and cared for, so he made the choice to fight him; however, it went terribly wrong for him, and his soul was destroyed.
Error, believing he was victorious, left, oblivious to the fact that a burst of Determination coming from Ink's connection to the multiverse kept him alive.
He retreated back to his timeline, where he isolated himself in fear Error would realize he had survived. There, he slowly lost his confidence, and questioned his role as a guardian. Dream eventually found him, though he was treated as a stranger by a distrustful Ink - since then, Dream's goal was to help Ink in any way he could.
After Dream managed to partially heal him via travelling through AUs, Dream made the mistake of leaving a portal to the Doodle Sphere open long enough for Error to find his way in. With Dream out of the way, as he had gone off to his own AU, Ink finally snapped seconds before Error killed him for good and fought against him again with renewed powers, requesting Dream not to intervene as he was fighting to fix his mistakes.
In the Bad Ending of the AU, Ink lost the final fight against Error, who went completely insane after destroying nearly every AU, and was killed. Dream tried to avenge him, but was apparently killed by Error too. It's a mildly open ending as what happens afterwards is not told.
In the True Ending of the AU, CORE!Frisk, knowing what had happened, brought people from the Omega Timeline who had been attacked by Error as well as others such as Geno and Fresh to stop him; Nightmare joined in as well, though not intending to help, nearly killing Error and Dream. Once he and Error finally left in defeat, Ink ended up dying, and Dream decided to stay in the Doodle Sphere.
His skull has several small cracks, and a larger one runs down his right eye, which he cannot open. The other eye's pupil is often in the shape of a teardrop, though it can change into a circle (if frightened) or a lightning bolt (if angered) as well as shapes that vary depending on what he feels.
Half of his scarf is burned off and his clothing has several small rips and burn marks. His paint vials are in a greyscale, and the heart-shaped tops are black.
His left arm is broken (specifically, the ulna is snapped in half) and he's constantly clutching it. Most of his ribs are cracked.
Once he began to heal on his own, his cracked eye could partially open, his ribs and ulna were no longer fractured and half of his vials regained their color, though they can revert if he's wounded again.
He's the exact opposite of what he used to be: easily frightened, distrustful, and with low self-esteem. He barely ever draws anymore due to his dwindling creativity after being isolated.
Trauma has made him unstable, and he is susceptible to reacting aggressively to anything that bothers or surprises him. Before Dream came along, he loathed the thought of having company.
He's depressed due to his failure, and constantly reminds himself that he's useless. He's way more forgetful than he used to be, also due to isolation.
Since his paintbrush was his main source of magic, his powers vary. His main attack consists of spirals created by his vials that shoot acidic paint. When reinforced by Determination, he can use more varied attacks, though only for a certain amount of time.
When not in a fight, he can still use his remaining art tools to bring paintings to life; however, they soon fade away, as Ink doesn't have enough motivation to make them persist. He does this when he feels too alone.
Despite being alive due to determination, he's not seen melting, but black ink will drip out of his eye crack if he's too nervous or angry. Sometimes, it happens at random intervals. When this happens, his voice will crackle, and his body will look like it's fading away. This causes him confusion and the inability to move properly, and hurts him.
His only attack costs him too much energy and concentration, so it's his last resort to use it.
He profusely hates him, but is at the same time afraid of him and of what he can do. His biggest fear is Error finding his timeline, event that did end up happening and went terribly wrong.
"what can i say, you got me impressed there. i really didn't think you could be any more stupid." - Error's mocking comments after Ink requested Dream not to help him fight.
Despite their friendship, Ink was heavily distrustful towards Dream when he came by, though they built trust back quickly. Dream cares a lot for wellbeing, helping and protecting him until the end, and Ink is greatly thankful to him.
"I w-want everything to just... g-go back to how it was b-before... I don't want to disappear... I... I don't want the multiverse to be gone..." - Ink to Dream, grieving about his failure.
Ink saved Frisk and Flowey from Error, unable to let himself stand and do nothing as an universe was destroyed in front of him. In the True Ending, they show their gratefulness to him and help in the fight against Error.
Prior to Ink and Error's first battle, Ink took Blueberry from the anti-void and brought him back to his brother. This, however, caused Error's hate towards Ink to grow.
He joined the fight against Error mostly to show his gratefulness to Ink for saving his brother, only having time to personally thank him right before he died.
- He is really prone to panic attacks and nightmares. These are the two main reasons of why the ink leaks that corrupt his body occur. Some of his nightmares are actually visions.
- He got the idea of writing a loose diary, something that eventually became really important to him. All the pages he wrote, however, were eventually destroyed except for one that Dream kept after Ink died.
- He has been mildly afraid of himself ever since his first mental breakdown, which nearly caused him to harm Outertale greatly.
- During the fight, the fact that he could use his paint vials to summon magic was unknown to him. It wasn't until he first snapped that he realized he was capable of it, so he has never gotten the chance to use it in battle.
- Even though drawing contributes to his stress, he is soothed by pastel colors, so he keeps reminding himself to use those if he has to draw anything.
- He doesn't tolerate anyone mentioning Error, not even himself.
- Dream has convinced him to occasionally visit several AUs once he realized that helped him greatly; the first they went to was Littletale.
- Even though he's aware of the universes that surround him, he keeps on forgetting which is which, or who inhabits them.
- To cope with his feeling of being a failure, he constantly reminds himself that he at least managed to prevent Underfell's destruction even if it almost ended with him killed.
- He has a hardly noticeable limp.
- He is aware of Broken Error's existence.
- He's forgotten almost everything that made him himself, and what he remembers the most are minor events of his past and the nightmares and visions he constantly has.
- He has a deep connection to the multiverse, but this doesn't always play in his favor as whenever an universe is destroyed, it greatly hurts him.
- Since his dust was sprayed all across his own timeline, he gained the ability to see and hear everything that goes on in it and may even manipulate things like weather, though there are heavy limits to his powers. He also regained his true personality after death.