Daniel's wussiness is a front.
He's actually a god, if not God Himself, but he has forgotten his powers. Later in the Game, he will remember his omnipotence, and completely crush Cancel.- Or he's actually a psychotic murderer who wants Kate all to himself, and wants to kill off the other contestants one by one. Particularly Seth. He was the first one to suggest killing Seth???, after all. Seth also accused him of stealing his medicine - although we don't know if this was true.
One of the Game participants is under an assumed identity.
That person is Joe, the "Poet from Nowhere." Camilla is stoic despite the monsters because...
she is actually an agent sent by the government, a la Dale Cooper or Francis York Morgan,to deal with unusual or supernatural cases. She is the Human Game player who has an assumed identity, and her training (somewhat) prepared her for this mission. She must rescue the hostages from Cancel and bring down the Achronists, but her weapons were confiscated when she joined the Game. Therefore, she must rely on the other Players' talents to stay alive. Cancel is a failed TV reality show host.
The Human Game is a last-ditch attempt to appeal to us, the audience, before the Achronists cut his funding. Kate is actually the mastermind behind the entire Human Game; unfortunately, she has amnesia and was accidentally placed in the Game herself.
She was secretly a mad scientist who wanted to destroy everyone she hated. Daniel is a pathetically obsessed paramour, Thalia is annoyingly popular and beautiful, Camilla disturbed her due to her stoic nature, Connor acted like a know-it-all grump, Abigail failed to hear Kate's (presumably dead) father, Seth is...well, Seth, and she sat next to Joe on the subway one time, and listened to him blabber on about poetry for an hour. So naturally, they all had to die. Cancel was a contestant in the last Human Game.
He lost. Cancel is actually extraordinarily beautiful, but he sadly doesn't know it.
He's been stuck in the facility for so long that he wants the company of others, but he's too embarrassed to show his face. He's also really bad at interacting with people, what with the whole kidnapping-and-torture business. It is up to the Human Game contestants to show him that true beauty lies on the inside, underneath his possibly parasitically-attached mask. The two Unknown Characters were once good friends.
One of them rescued the other from a life of homelessness, and they somehow began the Human Game. Unfortunately, the test subjects were treated poorly, and the former friends quickly became enemies. The Unknown Character who supported the Game became a monster - Cancel - and the rebellious one became the Painter, who put graffiti all over the facility walls before turning into another monster (possibly the one that was spying on the Players towards the beginning of the story. The Minims and Achronity, the computer, used to be human.
They lost the Human Game, or they were test subjects of the Achronists before the Game. There are multiple endings to the Human Game.
One of them will be a lighthearted anime high school parody, where all the Players are students and Cancel is their homeroom teacher with questionable teaching methods/overly strict principal. Sailor Senshi, kaiju, mechas, the power of friendship and tsunderes may or may not be involved. Something awful will happen to Daniel and/or Kate.
Possibly triggering the other to snap and become a monster. After all, she's been pretty protective of him so far, and he seems to view her as one of the only positive things in his life. So it's safe to say that losing one could hit the other hard. Joe will be the next one to break.
His lashing out when at the library and the accompanying headache do not spell out good things. All the symbols stand for different types of masks
The achronist blog calls them 'Null's. There are two classes known, which are 'Insect' (which is likely Seth's one) and 'the Wildcard' (which could very much be Daniel's one.)