Ninja Brian isn't a total psychopath, kinda
Every time you see Ninja Brain murder somebody it's when somebody invades his personal space such as the massacre at Club Foot in "Party of Three" or the meeting of Ninja Jim in "Best Friends Forever." Ninja Brian doesn't murder for fun, he murders because he has intense social anxiety and is severely threatened by others.- This is supported by the fact that he always spares Danny, his best friend. At least until the end of the video.
- "Feeling severely threatened by others" sounds more like paranoia than social anxiety. Someone with social anxiety fears public humiliation and rejection, while people with paranoia feel others are going to somehow hurt them.
Ninja Brian is a supernatural entity bound to Danny
In several songs, Danny Sexbang is shown to have at least rudimentary magical powers, though obviously not on Unicorn Wizard levels. It's possible that through some sort of wacky shenanigans, he ended up involved in the summoning of an ancient spirit of Ninja-osity intended to end the world by murdering literally everyone. Being the guy he is, he immediately decided to call this being Brian and that they were going to be best friends. This is why someone who can kill Slenderman and literally explode puppies with a thought is willing to do menial tasks. He cannot kill his master and must obey him, but that doesn't stop him from killing other people and generally screwing with the guy he's stuck with (not like that; unless his fanfiction is to be believed). He's also a physicist, because even nigh-omnipotent ninja demons need hobbies. Danny is actually Brian's ninja master
Everything from I Just Wanna (Dance) is true, and Danny Sexbang was once known as Ninja Danny. Ninja Brian, the second-toughest ninja ever, sought him out for training, but discovered to his dismay that he had given up the use of his ninja powers. Every interaction they have is based on Brian trying to force him to reveal his true power, so that they may have a proper ninja duel for the title of Toughest Fucking Ninja You've Ever Seen. Ninja Brian is cursed
(Taken from a post on a /tg/ thread that I started)Ninja Brian is cursed so he cannot permanently kill anyone he is hired to kill. In this case, someone put a hit on Danny, and Ninja Brian took the job. Now they just hang out and play music together while Brian repeatedly tries to kill Danny, who comes back to life every time. Danny really IS "the toughest fucking ninja"
Unlike Brian, whose primary strength is his ability to kill anyone, Danny's ninja power is his ability to survive anything people try to kill him with. This is either through sheer power of badass, or because he is so swift that he can replace himself with a lifelike dummy in the blink of an eye (which would provide an in-universe explanation for the Special Effect Failure in some of his death sequences).Furthermore, going from the Badass Decay evident in the later videos (see the YMMV page), we can assume that he is slowly losing his ninja powers from lack of use. Take the fact that he gets run over by a car and knocked off the road in "No Reason Boner" and is more worried about his boner, but by the time of "Cookies", he appears to be in pain when being consumed by demons (although he still survives, somehow).
Going with some of the above WMG, Ninja Brian and Ninja Danny were a tag-team of murder and mayhem. Presumably, Danny would act as bait and Brian would stab them while they were trying to beat Danny. That is, until Danny decided to give up his main job to focus on his love of dancing, and the NSP we see was begun.
- My interpretation was that at one point both Danny and Brian were ninjas, and somehow, at some point, each one was granted their heart's desire. Dan was granted immortality (and subsequently the ability to recover from any injury, making him the toughest fucking ninja), while Brian was granted the ultimate deadliness, able to kill anything and anyone in any way he wanted (making him the deadliest ninja). Eventually Dan decided to give up ninja-ing to pursue other interests like dancing and sex, while Brian became consumed with a desire to kill everything, except his best friend Danny. Usually.
Brian and Danny pulled a Jekyll and Hyde
They used to be one person but through the use of Ninja Sex magic turned his good side into his son that has retained partial memory of being the toughest ninja ever, but now lacks the skill to back up his statement and is why Ninja Brian is so over protective of Danny. Samurai Abstinence Patrol is responsible for human touch being made illegal by the year 6969
Foreshadowing a possible triumph over Ninja Sex Party in the future. Although it's possible that such extremes were never their intentions.- Two of the Dick Elders in the official 6969 MV
are played by Arin and Barry. Probably related?
Brian and Danny are actually 12 year olds writing these songs.
In the music canon for what it's worth these are two children trying to convey these ideas with their limited experiences. Let's get this terrible party started is because neither of them understands what makes for a good party, Dragon Slayer is about trying to impress a girl with what they think will impress her, so on and so forth. The 80s covers are because they're in the 80s and growing up with the music. And of course the swearing is because they're 12, 12 year old boys are obsessed with swearing. Danny is a Time Lord
But not just any Time Lord - the smarterest and most amazing of them all, the Unicorn Wizard. At the end of "Sex Training", Danny calls his student "the Lord of Vaginas and Time!", a clear hint that the Unicorn Wizard trained to become a Time Lord himself to be able to bestow such an incredible title. Apparently the Unicorn Wizard also trained to become a Vagina Lord, which must be another class of Gallifreyans Doctor Who simply hasn't revealed yet. He sings whole songs about how much he knows about creatures other people don't, like the Manticore and Rhinoceratops/Superpuma. He talks a lot about space and Time Travel, like in "Dinosaur Laser Fight", and how he killed a king to change European history in "I Just Want to (Dance)". In "Rhinoceratops vs. Superpuma", the President of Space even calls him and Ninja Brian for help and says they're the only ones who can, indicating that they are at least well known by aliens. In "Dragon Slayer", Danny says he lives in a huge mansion in space and in "6969", he builds his own time machine/space ship and even saves the future.Obviously Danny is a Time Lord - or was. Then he retired his title as Unicorn Wizard to live a quiet life as the toughest fucking ninja that you've ever seen. His knowledge of Time Travel made him a great assassin and Ninja Brian puts up with him for access to people in different times and places he ordinarily wouldn't be able to kill. Then Danny retired again, this time to become a singer and dancer. For now, he's Danny Sexbang, an ex-Time Lord, ex-ninja, dancing Lovable Sex Maniac.
Ninja Brian is vegan
Because Rule of Funny Ninja Brian was upset about the cake
The reason he beat The Necromancer to death (using Danny as a club) was for throwing his cake on the ground. Clearly a lot of thought and effort went into it, and Ninja Brian was upset at the rude gesture.