Jane Austen, introduced as an actual side character from the events of Saints Row IV, will narrate points of the story that take place in the large book that everything takes place in. The story starts at Kinzie's birthday party; she's never had one before, but everyone has a lot of fun regardless. Matt Miller gets the idea of using a Ouija board for fun, and asks the board if the President will ever get married. Shaundi asks who he'll marry, and the board responds with Jezebel, promptly leading up to the President being sucked into hell. After threatening the Ouija board itself, Johnny and Kinzie get sent to hell to search for the boss.
Welcome to Hell
The first thing you'll see in Hell is a billboard for the Ultor Corporation, which can't be a good thing. Steal a car from a dead husk nearby and then set your map to the Ultor building, so you know where to go by looking at the minimap. Inside the building is Dane Vogel, president of the company. After the three of them talk, it's revealed that, due to the destruction the boss has caused in their life, Satan wants them to marry his daughter, Jezebel. Gat's given the cracked halo of Lucifer, which will provide him powers similar to the superpowers in the previous game. Collect some soul clusters on the small island you appear on after talking with Dane. With these four clusters, you can buy some super spring and flight powers that you can use to get around. Test them out by jumping to the various islands marked on your screen; once you reach the last of the islands, Dane will fill you in on what to do next.
To attract Satan's attention, you'll need to cause mayhem throughout New Hades by doing activities, going on killing sprees, and other objectives in the quest log, inside the main menu. Now that you can freely run around hell, it'd be a good idea to either collect as many soul clusters as you can, or to gain some new allies in the underworld. Check the map first, where you'll see various red and blue markers; these are activities, and you can complete them to wrestle small portions of New Hades out of Satan's control. These can be made easier if you upgrade your Super Sprint and Flight as much as you can, so check the arcane upgrades list for some new and recently unlocked powers. Once you've decided what you want to do next, check the quest log and start it. If you decide to go for soul clusters first, you should try to get five in a row without touching the ground (made easier with a better Flight ability) for a missable achievement.
Collect at least five Soul Clusters without touching the ground
There are four places to go to, where you'll find people who will ally with you in your cause to kill Satan. Go to them in any order you please to not only increase your numbers, but also gain more powers for your halo.
The DeWynter sisters have been constantly under attack since they were both killed in Steelport; this is mainly because other strong business forces felt threatened by their success in the management world. Kill the few waves of demons that appear to safely bring them back to Dane in the Ultor Building, where they'll be offered 1/5 of the total revenue earned by taking down Satan. You'll also get the Blast power, which lets you launch balls of energy with various effects toward your foes. This first effect turns them into stone, which you can then shatter. Complete the nearby tutorial on Summons as part of the Arcane Lessons quest, so you don't have to come back here for it later.
Blackbeard will be aboard his ship, the Queen Anne's Revenge, when his ship has been boarded by imps. Shoot them with weapons, and more will show up from below decks. Grab God's Hammer from the chest at the stern, and use it to wipe out the rest of the little brats. These imps were actually summoned by Blackbeard himself, but they turned against him due to their natural hectic state. Once you save him and his ship, he'll agree to join the cause to kill Satan, but only because he's interested in the money he has. You'll also get the Summons power, which will allow you to summon imps of your own. Complete the nearby tutorial on Summons as part of the Arcane Lessons quest, so you don't have to come back here for it later.
Enter a prison where the marker to rally your next ally tells you to go. After a short walk in, you'll find a mental ward playing "The Wheels on the Bus". Poor Vlad the Impaler is stuck in the room, and will pass out due to the fatigue caused by the song and the room he's in. Quickly run over to him and revive him, then help him kill all of the demons holding him captive. Once the whole area is cleared out, there should be one enemy left: the DJ. He'll be jamming out hard in the booth on the highest level of the room. After turning off the music, you and Vlad will return to his castle, where he'll provide vital intel on Satan to the team. You'll also get the Aura ability; the first element you can use is Coldfire, which will set enemies on fire. Complete the nearby tutorial on Summons as part of the Arcane Lessons quest, so you don't have to come back here for it later.
Enter the Tempest, where William Shakespeare himself will become interested in the fact that you, a mortal, are walking around hell. He'll want to test your skill, so defeat the very weak amounts of enemies that appear. One enemy, the dark inciter, will be new to you. You'll have to shoot at its shield (or use a Blast attack) until you'll be able to hit him directly. It seems Shakespeare was cast out from Satan's palace for secretly tutoring Jezebel and re-enacting his old plays. To prove his loyalty to the cause, he'll give you the Stomp ability. Complete the nearby tutorial on Summons as part of the Arcane Lessons quest, so you don't have to come back here for it later.
Take a Break
After bringing your allies together, Dane Vogel will let you know that he found a very nice chair that he thinks you'd like. Head to its general location in the slums and look for a comfy recliner on a roof. It'll be a bit hard to spot, hidden in plain sight in front of a TV and next to a set of barrels that prop up a wooden plank to hold drinks on. Sit down, and you'll get one of the Seven Deadly Weapons, the Armchair-A-Geddon.
Once you hit Lv05 with your Saint after getting enough XP, you'll be treated with a musical number performed by Satan, Jezebel, Kinzie, and even Johnny. After you experience this masterpiece, Satan will plant over 20 spires around New Hades that shoot missiles at you when you're flying; this is obviously a problem. To disable one for good, you'll have to rip its heart out from the ground. Make sure you get the Top Gunner achievement out of the way before you destroy all of them, though. More detail on that achievement is on the Misc Achievements page.
Once you reach Lv10 with your Saint, Dane will call you over to the Ultor Building to meet a special guest. Jezebel will have come over to join Johnny in his quest to defeat her father. After Jezebel returns home, all of your friends will be captured by demons. Fly over to the places they're being held hostage at and free them by defeating the surrounding enemies. The main targets are the dark inciters keeping everyone in place; kill them and revive your homie, and the objective will be finished.
Crash the Wedding
At Lv15, Jezebel will be ready to sneak you into the palace. After Satan threatens to break Jezebel's neck, Gat will lay down his arms. The devil will take this as an act of love for his daughter, and will say that if Gat were to marry his daughter, he would return the President's soul. Johnny, a man of action, would much rather fight Satan instead of marrying a girl. Head to his balcony when you're prepared and get ready for a fight. I personally prefer using a souped-up Armchair-A-Geddon, as well as a strong Stone Blast.
Use whatever methods you like to take a large chunk of Satan's health away from him. When he's at about 60% health, he'll duplicate himself to make it harder to find him. After finding the real one, he'll send some enemies after you as he protects himself in a shield. Defeat the enemies to coax him out of his protection, and the cycle will repeat. Once Satan reaches 40% and 20% health, he'll use copies in an attempt to fool you once more. Taking his health down to these levels is still quite a lot of work, even with strong weapons, so chipping away at his health will take longer than you think.
After finally depleting all of Satan's health, run up to him and punch him in the face. After experiencing a humiliating defeat, Satan will banish Kinzie, Jezebel, and the President back to the mortal world. Johnny, though, has been stopped midway through the process by God, who says He owes him a favor for stopping Satan from invading heaven. You'll be able to choose from one of five endings; if you've played the first two Saints Row titles, one of these options should be more pleasing to you than the others. Choose whichever ending fits your fancy, and watch the cutscene that plays out the ending you chose. After it plays, the credits will roll (you can skip these if you want) and you should get the second of two story-based achievements.