Why does Snow Black not seem to have any problem with hooking up with Haruyuki despite his physical appearance? It's because of the fact that she's older than she looks thanks to Brain Burst, so she's developed past the point where she judges people based on looks or cares about what others think of her taste in romantic partners.
It's also possible that she can see her own pain in Haruyuki's due to what her and Black Vise's avatars imply the trauma for black colored avatars come from and what we've learned about her sister, White Cosmos. Her confession to Haruyuki seems to imply this too.
IIRC it's also because Haruu's cartoony-model is supposed to reflect his self-perception. In other words, he's not that fat or round irl. At the very least, he's Hollywood Pudgy.
Why does Brain Burst require its user to have worn a Neurolinker since birth? Because that's the only way it would be able to delete all the memories related to Brain Burst when it uninstalls itself. It makes sense that the Neurolinker is only able to tamper with memories that it was present for the creation of.
Why did Blue Knight decide to not use the Judgment Blow on Cyan Pile? If you remember what happened to Red Rider, he likely respects that Taku's reason for leaving was for the sake of a friend, and felt his reason was selfless enough to spare him.
More than the Neurolinker itself, what could happen if it were misused.
The Neurolinker can effectively hack sight, hearing, touch, smell, taste and time perception. This only can happen while the Neurolinker is connected to the brain, but...
...they are ubiquitous, to the point that even ID checking, or photographies transfer, is done via Neurolinker. At least in daily life, people use them constantly, and rarely put them off or remove them.
One of them is explicitly noted in the Light Novel, volume 3, chapter 6. After Haruyuki's augmented vision is hacked via a virus-infected picture, he notes that he could have perfectly been killed that way, if the hacker decided to make him misread the traffic lights.
And then there was the backdoor program that was installed in Chiyu's Neurolinker, which could allow the intruder to not only route his network connection through it, but to see and hear everything Chiyu does.
Short after Haruyuki meets Aqua Current, it's shown that the NL can selectively delete memories, presumably permanently. Also, in the first chapters it's shown it can read and interpret the fears and obsessions of its owner, so it should be possible to read any memory and release it to the global net, including passwords, pincodes, and criminal evidence.
Current is an exception since she did it via the Incarnate System, still a dangerous ability.
It's suspected, with the Chrome Disaster incident, that it can alter the personality of its owner.
Chrome Disaster is an exception, normal rules don't apply to it.
With all that said, simply removing the Neurolinker to never put it on again buffers you against all those dangers. The trouble is if you have been using it practically since birth.
This is probably why the predecessor, Brain Chip, is illegal. At the very least you can remove and switch off a Neurolinker. And both Kuroyukihime and Noumi shows that you can limit your Neurolinker's exposure to the outside world if you're very careful. (Noumi's case might be a bad example, as he only needs his Neurolinker/Brain Chip when he requires Brain Burst, and can use the other to function normally in the Neurolinked society)
Even then, literally almost all of society is based around Neurolinker interaction, from school curriculum to bank transactions to even unlocking the door to your own house. Operating without a Neurolinker would be the equivalent of being physically handicapped.
Based on Chiyu's reaction in episode 14 when Seiji sadistically demands that she become his pet and earlier remarks that a direct NL-to-NL cable connection is regarded as lovers-level of intimate, it is completely possible to commit cyber-rape through an NL.
Each linker's avatar, being born their fears and traumas, brings with it a whole host of fridge horror, some of which has been addressed in the series, but many have not, such as:
Black Lotus is impossible to grab or restrain. Just what could have happened to her that would make her produce such an avatar?
It could also be indicative of a belief that she can't touch anything without hurting it. Her hands are swords and the only reason Red Rider let her hug him was because that was about the only physical interaction she could achieve... and we all know what happened to him.
Red Rider's avatar was likely born from the feeling of everything in his life being out of reach or never being fast enough to get what he wanted or even needed, and wanting a way to reach it or be fast enough to get to it. Possibly explaining his possible ties to the Acceleration Research Society.
Yellow Radio is a Jester, who can cast illusions that make his injuries into fakes. In real life this would imply he's something of a Sad Clown, or even a Stepford Smiler. Even his avatar has a perpetual Theater Mask grin to it.
Crimson Kingbolt's ability is to take shattered and destroyed things and bring them all together into a single, stronger whole again. He comes from a broken home, one that apparently fell apart after he became a burst linker. What must that home life have been like, to instill him with such a desire?
Blood Leopard's special is to become an actual leopard, which she uses to brutally rip out people's throats and tear at their limbs. In addition she speaks in internet text shorthand and is rather socially inept, clear markers of a sociopath and someone who saw herself as a wild animal, not a human. Tellingly, she's the only linker so far whose "normal" avatar matches almost exactly to their Burst Avatar, both being Blood Red Leopards.
Aqua Current is made of water that lacks any impurities that could hold charged particles, making her immune to electricity. She's quiet and quiet smart, does her avatar's water body lack impurities because she was forced or felt she had to be perfect?
Sky Raker was a girl without legs who could walk thanks to science, yet her avatar was intact and designed for a part of the world that didn't even exist yet. Even though she could pass as normal, her missing limbs clearly affected how alienated she felt from the rest of the world.
Ardor Maiden is one of only two Avatars to have two colors (red and white in her case) represent their avatar. This is because her trauma is divided between who she is and her wish to be a Noh performer, and who her family will allow her to be due to their traditions.
Using the above white as an example, White Cosmos' duel avatar was likely the result of her family and others deciding everything on everything in her life. This leads to her becoming the cruelpresident of the Acceleration Research Society to finally be the one in control, possibly including manipulating her sister so avatar's color would become black.
Rust Jigsaw is pretty self explanatory...he's a slasher film incarnate, capable of setting up razor wire traps and throwing circular saws capable of bisecting buildings at people. What horror could have produced someone like that?
Green Grandee is functionally invulnerable...perhaps because he was frequently beaten or otherwise injured, that would cause his avatar to manifest an absolute defense.
Blue Knight's may be a variation on what created Cyan Pile, he was picked on for being weak or even physically attacked which developed in anger and strength to defeat all who mocked him. This caused his Avatar to become powerful enough he could defeat legendary beasts by himself.
Purple Thorn's an avatar that can attack from any direction or distance, with the thorn part of her name it's likely she's so paranoid of everything she let's nearly no one get close to her and is alert to everything around her. This likely also explains her jealousy when Black Thorn got too close to Red Rider.
That one avatar who shocked Silver Crow in the Unlimited Field used a move called "Electric Therapy". The avatars appearance and the name of the move has some verydisturbing implications.
The system that decides a player's Avatar color ends up this way when you recall it does so by the focus of their trauma, and therefore gives a general idea of what said trauma is.
Red avatars focus on long-distance attacks, meaning traumas related to them relate to the player distancing themselves or wanting to reach for something faraway or out of their reach.
Green avatars focus on defense and protection, so traumas related to them are ones that make the player feel vulnerable or like they need to be shielded, or wanting to protect people important to them.
Blue avatars focus on close-combat, so traumas related to them are often the result of wanting to overcome obstacles or gaining strength where one feels they are weak and/or powerless.
Yellow avatars focus on jamming abilities to defend from a distance, so traumas related to them are likely those who feel the need to fool others to how they really feel and look like something they're not.
Purple avatars focus on multi-range attacks but also lacking defense in exchange, so traumas related to them are probably those who feel they can't defend or protect themselves and need to be aware of everything around them, no how close or far away they are.
While the traumas related black avatars are unknown, Black Lotus and Black Vise both have abilities that restrict other players' abilities, attacks and movements. In the color spectrum, black is the absence of color, so it's likely their traumas relate to loneliness and fear.
Based on the white half of Ardor Maiden and White Cosmos' abilities, it's likely the traumas of white avatars are related to feeling their life being manipulated and controlled by outside sources or even other people and being confused on what they feel, mixing all the colors on the spectrum together to create white.
Metal avatars are where the worst traumas tend to be, said to be created from the player having strong walls around their heart. This gets worse when it's shown that metal avatars can actually be forcefully made by others' affecting a future player's environment.
Chrome Falcon used incarnate to produce the Chrome Disaster armor because of his anguish over the loss of his love. Now remember that all 7 kings know how to use incarnate, and none of them want to lose brain burst. So great is their desire not to lose acceleration that they've established a meta peace treaty outside the basic limits of the game itself. Now imagine what would happen if they were defeated while overwhelmed by their desire to endure. Each king is basically another Chrome Disaster waiting to happen.
The fact that some Metal colored avatars are being made by people manipulating one's environment in the real world before they get brain burst installed, especially by the Acceleration Research Society, and that there might be bullies much worse than Araya.
This is especially chilling when we're introduced to Wolfram Cerberus, who has three personalities that give him tons of abilities for his Duel Avatar and has been manipulated to the point he can't escape the ARS' psychological grasp on him. What kind of experiences were forced on him to create those other two personalities?
While we've yet to see any examples in-story, what if those who go through this end up either failing to install brain burst successfully or refuse to install it? They ended up going through all that suffering for nothing, and worse... the people who out them through all of it may not even care.
If Haru and Taku had lost their duel to Noumi, he could very well have decided that since they were no longer useful to him, there was no reason for him not to report Haru for planting the camera inside the girls' shower room, thereby resulting in Haru getting expelled.