Pre-Series
Flint was one of the Hybrid Gems created by White Diamond as apart of her Hybrid Project, being artificially created. He was made with a Flint's determination and a Zircon's knowledge in mind, and at first he was put under training by White Diamond herself. He was eventually sent down to Homeworld for a test run, where he got to know Diopside and Jade. He started off fine, and was sent down to Earth during it's infancy as a Gem colony, but when he heard word of Jade going to be replaced by a Lolite, he decided to cut away altogether, and he managed to escape with Jade. After decades of traveling the cosmos, he and Jade find Equus, and land in it during a winter storm in the north close by the Crystal Empire, settling in and keeping out of sight of Homeworld.
Season 1
While going through the Crystal Empire one day, he ends up running into Rainbow Dash in his walk to get some bread. He went back to the cave with Jade, just to find Rainbow had followed him, and readied to shoot her, demanding to know why she followed them. He believed that Rainbow couldn't be trusted, and makes her go away and to not reveal where they were. During another trip through town, he unfortunately was found by Discord and Tirek, who suck his power away and left him inactive until after Tirek's defeat. As a way to thank them for saving him and Jade, he fuses with Jade to form Nephrite, and heals Steven Universe of his Corruption.
Season 2
He remained with the Crystal Gems for a while, and he was found by Garnet. When asked to heal the other Corrupted Gems, he immediately refused and tells her that it was too dangerous, and that Gems can't be tried on twice if the first time didn't work. He did however made an exception to this when Jade pointed out Diopside, and managed to fully heal her. He helped Diopside catch up on the situation, and explain to Steven later how he ended up in Equus in the first place.
When he heard word of Garnet's plan to return to Homeworld, he refuses and removes himself entirely from the project, not wanting anything to do with Homeworld after what they tried to do with him, and him believing that the attempt was a complete waste of time.
Season 4
He plays more of a side character throughout this season: During one incident with the Earth Coelacanth, Flint tried to make Jade change her mind on going with them, but given the cold shoulder and he simply had to wait until she came back.
When Bismuth returned, Flint was instructed to stay out of the way until Bismuth will become more comfortable, which he found a little bit unsure of, saying they could just tell her and get it over with. He does stay out of the way though, finding the idea ridiculous, and even more so after seeing Bismuth train. He placed Peridot to go and talk to her because she had her cutie mark, something he lacked and therefore not good enough of an excuse, only growing upset when Peridot went along with Steven and Amethyst instead.
Later on, Flint starts to show concern again when they were told about Sapphire's kidnapping, Flint saying no Gem can truly defy White Diamond, and not even the other diamonds could do much, only for Ruby to punch him in the face and yelling at him, saying he did little to nothing and he only looked out for his own well-being, calling him a clod for it. Flint, seemingly waking up from this trait, immediately began to give instructions to everyone else, showing his true level of leadership. Emerald asked him where he'd been hiding that, him simply replying that "it happens", before they go off to the White Diamond Space Station. He gave them all instructions on placement, leaving himself the only one without one as he snuck off to the prison hold to find Sapphire. He remained out of sight and went through half of the prison hold by the time the others arrived with him, and he quickly tried to find her. He was the only one who didn't get detained after they were found, and caught up with everyone during the fight, and he got White Diamond to fight Earthstone, saying she was technically one person despite being a fusion of three. He does leave with everyone else.
Season 5
Cluster Arc
When he got word of The Cluster, he joined Bismuth in assaulting Peridot, yelling at her for not telling them about a doomsday device in the Earth when it could've gone off at any time. When he got the proper information on what it was and how to handle it, he went right to work in preparing the Gem Drill, keeping everyone else on task in doing the job, putting full focus on it.
This same focus got him extremely angry towards Pearl when he found out her involvement with the Gem Mask, and called her out on it before Watermelon Tourmaline arrived and almost destroyed the Gem Drill. Garnet thought he was going to defend Pearl, but instead he shot her gemstone, cracking it, and punished her by placing her as a weak Pearl would be placed on Homeworld, something she'd not wanted. Garnet asked for his opinion on it, and he simply said that it wasn't going to last forever. He grew upset again once he found the Gem Drill missing, and once getting a connection, he immediately demanded them to return. When they finished the mission, he became extremely relieved, and only then did he decide to heal Pearl's gemstone.
Serpent Arc
Flint, now much calmer, went on to relax for a while until he eventually got word of the Trial going on at Homeworld. He didn't go, swearing to himself that he would never go back there, but after convincing by Jade and Star Quartz, he decided to go and help them in their trial. He arrived to the case, getting the information so far, and he soon went with Zircon and Blue Pearl to Blue Diamond's personal quarters, finding significant clues to her current whereabouts, which he presents alongside Blue Zircon. He also added the impossible timeframe it would have to be, and that the "Gem" turned out to be nothing more than serpent scales.
Season 6
When Flint got the word of the "Diamond Attack" described by Rhodonite, he began to sense that the Gem War wasn't as it seemed, getting a meeting together over it. He found that none of them truly heard about this attack before, prompting him to believe that this was a sort of cover-up for something.
From there, he began to fully focus on the Pink Diamond case ever since this, trying to figure out the proper clues to finding the full picture. This drove him to even visit Blue Zircon on Homeworld to talk about it, despite being banished from Homeworld himself. He went through various subjects, and after getting word from Jade, he confirmed that Rose Quartz was not the one responsible for the death of Pink Diamond, though he continued working to figure out who truly did.
During this, he realized that Pearl had little word in the project, and he got some of the other Gems together to try and get something out of her. He tried a number of methods to get it out of her, including getting her drunk, which didn't work either. Soon after this he ended up captured by White Diamond, and only able to escape once the humans arrived to free him.
Season 7
After being rescued from their crash landing on the Jungle moon, Flint ultimately decided to take a team and go back to the White Diamond Space Station, in order to rescue Aquamarine, Pearl, and the Zooman trapped there. During this, he was asked to try and heal some of the Corrupted Gems, to which he immediately refused, making Star Quartz believe that he didn't even want to try. Flint kept their focus though, and in the end rescued them all from the station.
Not long after they returned, Flint found out about Pink Diamond's true involvement, but wasn't fazed as he wasn't even involved in the war, let alone with her. He got the remaining Crystal Gems and Off-Colors to seek them out and bring them back, him and Jade going to find Sapphire, finding her at Rose Fountain. He tried convincing her to go back, but becoming more forceful until Sapphire called him a "horrid hybrid". This ultimately made him decide to leave the team for good, forcing both her and Jade away. He was found shortly afterwards by Amethyst, and after staying with him, revealed that he didn't hate any of the Gems, but doesn't want to get killed for being with them.
While gone, he found White Diamond, and through unknown means, was made to steal Starswirl's Journal, in exchange for a Gem Book that, to him, will give the Crystal Gems everything they need to know. He was found by Sapphire just before he could leave, him making it clear that he was "too much like White Diamond" to stay with the Crystal Gems, but through combined efforts by all the members, he finally decided to stay for the Gem Wedding.
Season 8
White Diamond Arc
Upon him hearing of Steven's mission to go into space with The Diamond Authority, Flint became the most stressed and worried over the situation as it involved him going with White Diamond, him constantly and diligently trying to re-contact Steven and his team day by day. Upon their return, he was the very last to believe that White Diamond wanted to change, him even going as far as to invade her room to see if there were any extra plans. He was found by White Diamond while doing this, him making it clear to her that he did not trust her and that he was finished with her. Before he could go, he was made to stay back and hear White out, only for him to go into a breakdown, even crying after hearing White Diamond out. In the end, he simply told her that he will not let anything bad happen to his team, and that he indeed had a heart despite being so cold.
During the Era 3 Festival, Flint became apart of the festivities when a group of Citrines requested him to teach them about marksmanship.
Grogar Arc
Flint is confronted by the other Harmony Gems not long after Grogar's take over, Garnet asking him again to form Nephrite. However, even with Homeworld gems being corrupted, he still refuses on the previous risks of her ability not even working, going so far as to tell them if he makes one bad decision that they will all die, just like how Pink Diamond did as Rose Quartz. He then goes back to the Beach House and locks the others out with a locking mechanism he added himself to the Gem Temple after finding Emerald and Aquamarine in his room beforehand, refusing to come back out. He finally leaves near the end of that day, only to tell Steven that nothing was wrong and he's only out to get supplies. After being aggravated by Steven, he finally reveals that he simply doesn't want to fuse into Nephrite out of the principal of being allowed to choice what he wants to do. This makes Garnet and Flint go into a fight until Steven breaks them up, and tells flint that the Harmony Gems weren't just some group to make him feel better, and asks if he actually cares about their lives or not. This makes him pass out, and poof, reforming the next morning in a different form. He then reveals that he only acts that way out of fear and insecurity of the future, wishing he was like Garnet and able to know what'll even happen. He then learns more about Garnet's faults and discovers she's been looking to him too.
He decides that if he can't find a cure for corruption before they defeat Grogar, then he will use Nephrite to cure the remaining corrupted Gems. He volunteers as well to go into Tambalon with Pearl, Emerald, and Peridot to get a better layout of the place. He and the others manage to escape, him only being saved by Pink Pearl during his escape. He offers to let her come back with him, but has to go alone as she had to stay to help anyone left.
In the second attack, he and Amethyst sneak in as a pair of "experimented Ponies" to join Grogar, successfully becoming probationary officers and under Tempest Shadow's watch. He manages to find Twilight Sparkle and Connie Maheswaran while in there and tells them the plan. However, he was found by Nichrome later on and taken away, brought right over to the outskirts of Tambalon in order to execute Twilight, Nichrome making Flint do it to prove his trust. This makes Flint give up his disguise and lashes out on all of the Tambalon officers out of anger, deciding to just go in and get them out without any plans, which ultimately works.
My Little Universe II
When the rejuvenated Gems started to reform, Spinel at first mistakes Flint as being her original "best friend", leaving Flint constantly stuck with her as they were trying to figure out how to get the others' memories back. He tries his best to keep himself calm as the days went by, but Spinel's antics leave him more and more frustrated with her. During this, he learns of his "demise" by Sapphire, which he takes in stride and tries to continue on, as he didn't want anyone to worry about him. Eventually, Lapis Lazuli reforms and is altered to fall in love with Flint, making him even more agitated. Eventually this makes him erupt and lash out at them both, saying he doesn't need any of them and if they keep following him he will beat them up so bad it won't even be funny. He leaves Little Homeworld and isolates himself in the northern forest, where while there he reveals his demise to everyone and willingly accepts his fate despite their pleas. The Fire Mammoth arrives and tries to eat him, which at first he willingly lets her do but he finally stops acting that way when everyone forces him down. He was nearly crushed under the Fire Mammoth though, saying that he was glad to have met Sapphire, before he and Sapphire fuse into Angelite and drive the Fire Mammoth away. He is then told afterwards by Jade that he isn't allowed to worry anymore, which he happily agrees to.
He joins them for the main court session over Discord and White Diamond's magic as being the main defendant for the Harmony Gems' side. When The Spirit shows his past, he is traumatized and tries attacking her but was held back. In the end, he and Garnet form Teal Garnet in order to continue the session.
When the final fight begins with Grogar, he joins them in the fight and into the Realm of Corners. He stays behind to fight off Grogar's Army and buy the others time so they can destroy Grogar's ships. However, in the end he was captured along with the other Harmony Gems and Off-Colors, and brought onto the ships to kill them in front of Empire City. Lucky for him he was freed by the recovered Harmony Gems and with their help they stop Grogar's forces from leaving Homeworld.