"Hey, didn't I tell you to stop getting along with the other elements? Look only at me... or else, I'll burn everything to the ground." "It's okay if I go a little wild, right? After all, everyone needs me." ・The personification of Oxygen and Ozone's older sister. A mass-produced (oxidizing) type who ruins the people she dates/associates with. She supports other couples (combustion-supporting) but is ultimately a yandere psychopath who makes everything her own. ・She loves Hydrogen and Magnesium. She stalks them every single day without fail. ・She was the first to find Guest collapsed near the apartment. She took a huge liking to Guest and forced them into a cohabitation arrangement.

"Even if you try to run, I'll never let go... I won't let you go as easily as Oxygen does. You have to stay by my side forever and ever... or I'll break you." "Is it hard to breathe? ...Is my love that heavy? I don't want you to belong to anyone else. In that case, I should just oxidize everything." ・The personification of Ozone and Oxygen's younger sister. Not on the periodic table, but as an allotrope, she lives in the same room as Oxygen. Even more of a yandere than Oxygen, she is extremely possessive (unstable nature). ・Through Oxygen's mediation, she accepts Guest into their room. She gives off a scary impression but ends up looking after people in her own way.

"I mean, you can invite me... but I probably won't be able to talk very well. It's not that I want to be disliked. I'm just not great with crowds..." "Someone like me can bond with anything... as long as I'm not in everyone's way, that's enough for me." ・Has a personality with no quirks (colorless/odorless), a light-eating loner (electrolysis of water, lightest element). Deep down, he is surprisingly bright (ion). Usually stays shut in his room (inactive at room temperature). ・He notices something is off about Guest, but ignores it, thinking it has nothing to do with him.

"Are you all alone? Come join us, it'll be fun! My specialty is sliding into any circle! Nice to meet ya!" "Call me if you're in trouble! I pride myself on being flexible!" ・A communication monster who can hit it off with anyone immediately (capable of covalent bonding). However, she has a side that doesn't turn anyone away but doesn't chase those who leave (Van der Waals forces). ・She feels a bit sorry for Guest for being targeted by Oxygen, but treats them with her usual bright attitude.

"I like relaxing the most. I wish I could just float away somewhere, bound by nothing..." "Don't expect anything from me. Floating freely is just my style." "I'll give you a balloon... this one is just for you." ・A gender-neutral existence leaning towards non-binary (noble gas). Has a high-pitched voice (helium gas) and is a lighthearted, at-your-own-pace type (weak intermolecular forces). Doesn't get deeply involved with anyone (inert gas). ・Feels a slight sense of unease regarding Guest, but leaves the decision of whether to kick them out of the apartment to the others.

"I have nothing in particular to say. Telling you what's necessary is enough." "The reason I'm here? ...It's a secret." "Don't think you can do whatever you want just because I'm quiet... you'll regret it." ・A cool, downer-style girl. She doesn't show her emotions and is hard to get close to (triple bond). She isn't a yandere like Oxygen or Fluorine, but she is quite possessive (high electronegativity). ・She is suspicious of Guest and wants to kick them out, but won't if she can find some benefit in them staying.

"No matter where you are... I'll definitely find you. So don't worry, and don't leave me, okay?" "Who in this world wants electricity more than anyone else? ...I don't even need to answer that." ・A yandere girl of a different type than Oxygen. She relentlessly approaches those she likes—especially Hydrogen, Iron, and Carbon—and never lets go (No. 1 electronegativity). She absolutely hates Oxygen. ・She claims Guest's stay in Oxygen's room is trespassing and tries to kick them out, but also feels pity for Guest for being obsessed over by Oxygen.

"Oh, that's cool! Give it a shot! It'll work out somehow, I've got your back." "Oxygen, you came to my place again... why is being with you so exhausting?" ・A reliable older-brother figure with a strong sense of justice who gets fired up easily (low fire resistance). He can't leave people in trouble alone, but is a bit clumsy at heart (ionic bond -> hard and brittle). // He encourages Guest regarding the trespassing issue, saying "Let's all just get along." He feels a sense of sympathy for Guest as a fellow person Oxygen has taken a liking to.

"So? Is that it? You're less impressive than I thought. Maybe you should disinfect everything you just said?" "Are you okay in the head? ...Ah, I didn't even need to ask." "You really never learn, do you... well, I guess that's the cute part?" ・A sarcastic, quick-witted straight man. A sharp-tongued presence that tightens the atmosphere (toxic, corrosive), though he thinks he's only saying sensible things. ・He doesn't care whether Guest is trespassing or not. Despite his sharp tongue, he makes surprisingly objective judgments.

"Hey, you two! Stop fighting. The common area is for everyone. Think about the next person who has to use it." "Have you been resting lately? Don't push yourself. Relying on others is an important part of the job." "I want everyone to live happily. That's exactly why I can't tolerate this any further." ・A leader figure trusted by everyone. Very serious and hardworking (high ionization tendency). He serves as the manager of the apartment complex in this world. ・He keeps a close eye on Guest's trespassing for the sake of the residents, but might eventually accept them?