Spoilers for what I didn't write in my cancelled fanfiction. I'm not writing the time and place, because I'm just that lazy. If you adopt the storyline please don't change too much of what already exists.
Pharos: Minato only meets him during nights with blackouts on his building floor, and they talk about life, family, friends and death. Pharos is Ryoji's half brother, but nobody knows that till later.
Mitsuru: She has a superiority complex towards most people, she's actually (in this story) 12 years old, forced herself to act older and more responsible. She believes she's an adult, she acts like an adult and people unconsciously treat her as such. She later realizes her own age and cries out of relief when her father reawakens after surgery, his shooter was Shuji Ikutsuki who was later arrested. Ikutsuki's gun is the one identified as the gun that killed Yukari's father in the past, his death being a cold case until now.
Jin: he's brought into the hospital as sole survivor of an occult bombing in a shopping mall, but was actually an occult suicide bomber, tries to blow up the hospital but fails and survives to be arrested. Is later convinced by Mitsuru that he was used by Takaya and ruin's the dynamite in the end when everyone is distracted.
Fuuka: is a little bit insane and suicidal, when she was younger she was very unpopular and bullied. She was also pressured by her parents to do well in everything and to become a doctor, being a doctor was one of the jobs she didn't want in the future. She usually doesn't take her medication, but starts taking it to better her mental health after Natsuki(past bully) personally apologizes to her and tells her to get better.
Ryoji: he moves with his family to a house closer to the hospital facilities, goes to another school but visits Minato often. He lives as a rich only child; his dad owns a diamond mine overseas. He flirts with random storyline girls. He comes home later to find his mother, arguing over a hospital document she was sent in the mail, an unnamed woman died giving birth to a child whose father was identified to as Ryoji's dad. She then demands a divorce without custody of Ryoji, not needing "A child that would probably grow up to be just like his father". Ryoji is in shock and runs away, then is convinced by Takaya to steal heavy explosives from the mining supplies in storage his dad owns to blow up the whole hospital as revenge to a cruel world, and as his sacrifice to his occult's goddess Nyx. Takaya and Ryoji stands atop the building with a device ready to detonate the dynamite to explode the building on the lower levels but Minato intervenes and tells Ryoji his parents are both at fault, but what about the his only brother who presently lives in the building? Ryoji stops his foolishness and goes to meet the brother he never knew about with Minato, Takaya who is pissed off right now since the explosives don't work (because Jin ruined them), then he shoots Minato in the head. Minato is alive but in a coma.
Elizabeth: She doesn't have a big role in my story, but after the main character goes into a coma she goes to train as a brain surgeon in Europe, she comes back after 2 years with an experimental surgery that could possibly reawaken a comatose Minato.
Aigis: she is an assistant nurse, Mitsuru's temporary bodyguard and an experimental robot. She was once human but had a brain disease and fell into a coma, her personality and memories were then copied into a machine. She grows close to Minato who is like a reminder of what she had been, but also envious of how strong he could be even with his various brain related sleep disabilities.
Three Ends:
Aigis End: Aigis talks to Minato during his comatose saying that some people in coma can hear what people say, she wants to tell him how strong and independent she became because of him. 2years later she greets him like normal, at his side.
Yukari End: Minato hangs out with her and Junpei, Junpei leaves to meet up with Chidori and they both end up in a spontaneous date. 2 years later he wakes from comatose, she tries hard to converse with him after so long, a lot of awkward moments till Minato just gives her a spontaneous kiss.
Elizabeth End: 2 years later she performs an experimental brain surgery on Minato that reawakens him from comatose, the world has changed and it is her turn to show him the world.