In Chapter 4, "Meet your Master", "You" is teleported to a cave network in the Draco Grasslands. Upon arriving, he loses contact with the King, and fights his way out of the caves. Upon exiting the caves, he spots a castle in the clearing, and makes his way inside. "You" is greeted by the King himself, along with the four Masters. After explaining who the masters are and the strengths/weaknesses of each class, the King reveals that a factory has just been constructed that is jamming his magic communication, and transports "You" to the factory.
These are the bosses fought in Chapter 4 of BFSR. This chapter only includes 2 boss fights, which is the least out of all of the chapters. Chapter 4 is also the first chapter in the game to include a boss with a healing skill, which is Aqua. Bosses are listed in order you fight them:
"You" is teleported into a cave network under the Draco Grasslands. A single tunnel at the far end of the cave leads to the next room.
-You: "Okay... Seems we're out of that weird place."
-You: "King? Do you know where my location is now?"
-You: "Seems I'm on my own for now."
-You: "Have to be on the lookout for any monsters that could be lurking around..."
-You: "Here come some enemies!
Rock monsters spawn at the end of the hallway.
"You" defeats the rock monsters.
-You: "Wheew. That was a lot of enemies."
-You: "Oh. You must be the leader."
-You: "Well okay. Bring it on!"
"You" defeats Stone.
-You: "Damn, that guy was tough."
-You: "Hey, I can continue now!"
"You" continues through the passage at the end of the cave, which leads him into a cave flooded to the waist-level with water.
-You: "Ugh. Now I'm soaked."
-You: "And now water monsters, fantastic."
Water monsters spawn in the cave.
"You" defeats the water monsters.
-You: "Alright, I know how this works now. Where's the leader."
-Aqua: "Seems my rocky friend couldn't defeat you."
-Aqua: "He was so stupid and slow... He couldn't even talk!"
-You: "He did seem a bit. Stone cold :)"
-Aqua: "I'm going to have a bit more fun drowning you now."
"You" defeats Aqua.
-Aqua: "Ugh... Darn you..."
-You: "I guess you could say they're all..."
-You: "...washed up."
-You: "Why am I making jokes to myself..."
-You: "I should get going."
"You" follows the water and are greeted with a sheer cliff with bits of rock jutting out of it.
-You: "Guess the water trails of here..."
-You: "I gotta get up there!"
-You: "This is going to be one heck of a climb!"
"You" climbs to the top of the cliff and exit the cave network. He is greeted by another cliff face with a castle on the plateau above.
-You: "Alright, now I need to get up THERE."
Armored Monsters arrive.
-You: "Damn, more monsters, I'll finish them and worry about how to get up there later!"
"You" defeats the Armored Monsters.
-You: "It's honestly odd just how many enemies are in this area."
-You: "I just hope that was all of them."
-You: "Huh, what's this?"
-You: "I can get up there now!"
The castle's door starts opening.
-You: "The door is opening too! Gotta get through before it closes!"
"You" makes it through the castle door and are greeted by the King and the Masters.
-You: "King, is that you?!"
-You: "Where were you?"
-King: "I've always been here, I just use magic to talk to you from afar."
-You: "Oh... That makes a lot of sense..."
-You: "But how come you didn't talk to me before?"
-King："I'll get to that now. There is a factory that has just been built. It seems to be jamming my magic communication."
-King: "I want you to go shut down that place so we have a way of communicating again."
-You: "Okay. Who are these guys though?"
-King: "These are the masters."
-Baller: "Who are we? Who are YOU?"
-Piercer: "We are the original creators of the weapons you use."
-Crusher: "Yeah! We're also the best at using them too!"
-Slicer: "We've become quite strong over time."
-Slicer: "We'll each give you a brief overview of our stats."
-Slicer: "To start, I'm Slicer. I'm what they call the jack of all trades."
-Slicer: "I'm not bad at anything, but I'm not necessarily the best either."
-Crusher: "I'll go next!"
-Crusher: "I'm CRUSHER!"
-Crusher: "I can dish out incredible damage, and take a lot of it too!"
-Crusher: "I'm quite slow though."
-Piercer: "I'll go next."
-Piercer: "My name is piercer."
-Piercer: "Nothing can escape my bow's range and accuracy."
-Piercer: "I can also take more damage than Baller."
-Piercer: "I'm slightly slower than him though."
-Piercer: "I deal the least damage out of everyone."
-Baller: "Best 'till last!"
-Baller: "I'm the fastest class, and can deal as much damage as slicer!"
-Baller: "I have good range, but not as much accuracy as Piercer."
-Baller: "My only flaw is, I hate to say it but,"
-Baller: "I can't take too much damage."
-King: "That's all of them!"
-King: "Back to objectives."
-King: "Quite conveniently, they missed out my transportation magic!"
-King: "I'll send you to the factory."
-Server: "Chapter 4 [Complete]: Meet the Masters."
-Server: "Fifth Area: Laser Generator Factory."
"You" is teleported to the next area.
-Aqua's boss battle used to be buffed extremely in early versions of BFSR. He used to shoot bullets whenever players respawn. The bullets would go through FF and were only dodgeable with precise timing. This made him harder than Duo Crisis. Luckily, he has since been nerfed.
-Stone used to have a bug where he would knock the player back if they got too close. This has been fixed in BFSR.
-Pre-rebirth, the king would also explain how bosses would emit a colored shockwave to indicate that they would attack. This has been skipped over in BFSR.
-In the throne room, the masters' pedestals are arranged BSCP, however, their official order is BPSC.
-Chapter 4 is tied with chapter 5 and 6 for the fewest individual bosses out of any chapter.
-There is a typo when Water Monsters spawn, where the objective says "Defeat the Rock Monsters".
-Aqua's heal heals 3600hp at a time, but he heals 4 times at once, amounting to 14400 hp healed.