
Reze is not coming back bro. She's dead. Denjis only remembering her after he threw up Bitterness devil, he remembered the bitter coffee he had with her.
Shes dead.

Katana man didn't come back the devil was put in another body. Each time Katana man has come back you can see differences in his outfit. You can even see a bomb lady after Reze died in chapter 87 even though she looks like Reze. It doesn't really matter as she dies in chapter 89 along other devilhhybridswhich haven't been seen. The only devil that died there and came back is Maxima

the only mentionable way of seeing Reze again is by reading Goodbye Eri. As the characters share some similarities. the mysterious girls which understands the protagonist you could even point out that both Eri and Reze didn't go to school.
Fujimoto has already foreshadowed characters like Nayuta in Nayyuta of the prophecy. Or love is blind where you could draw similarities to Aki and himeno a couple who was being interrupted by the end of the with out going out once

I'm not smart enough to understand what's going on

This is half spoiler half connection point, but since Sekhemet, Godess of destruction, is on the mirror, its safe to assume the mirror originated from her. With that information, lets backtrack a couple hundred years: Sekhemet tricked Nep and made her look into the mirror, which then caused the false Nep to become fertilized with Anubis through Osiris' seed, flash forward a couple centuries later and now Hathor has the mirror but failed to use it and synced it up with Seth and Horus. Her intention was to use it for Horus so that they could sleep together because she wanted to secure the crown and she genuinely likes Horus. The mirror, I presume, causes uncontrollable infatuation between two people who look into it. This is evident in Horus raping Seth and then being in a state of disarray afterwards. No one knows of the exact origin, nor why its linked to Chaos. I hope this helped just a little bit :"v

I'll try to elaborate onto this in bullet points!
1. There are two mirrors one for sekhmet one for hator. The two of them have different power abilities which I'm also not sure of/kinda forgot
The sekhmet one apparently traps ppl inside the mirror if the person whose face u see isn't the person u genuinely love.
Now the next part is a future spoiler so pls skip if u don't want it. But the reason nephythis is inside that mirror cuz during their harmonious reign Osiris got that mirror n placed it strategically so that it looked like offering tribute and wanted Seth to use it n see him so that og Seth would get trapped inside the mirror and the version outside will fall in love with Osiris or get brainwashed magically. But nephyths accidentally uses the mirror and sees Osiris in it. Now nephythis innermost desire was to have a child so that she can be more bonded down Seth who's alrdy her husband and in her trance a part of her heart gets trapped inside the mirror which we can say is the og nephyths n the one outside is the one that approached Osiris n struck a deal with him. She took his seed n bore anubis in exchange for granting Osiris the power of bringing life since male gods can't have kids but Osiris wanted to have a child with Seth because of twisted reasons you'll read in details in future chapters. But Osiris fails to create such a child using Seth's sperm so he plans to kill anubis n use his body as a vessel to host the child he plans to bring in this world. Seth pleads n begs against this n agrees to being raped by Osiris.
2. The other mirror is hators mirror n she gifted it to horus but he saw Seth in it n since he genuinely loved Seth he wasn't trapped in it but his darkest emotion n urges got amplified n he raped Seth against his wishes (like nephyths with Osiris)
Now to brief a bit on the theories in comment section
You see, the murals and hieroglyphics throughout ennead since chp1 till now aren't random drawings tye author made for background aesthetics but they're actually legit and readable and are literal spoilers for the plot. The murals that horus n nephythis are now reading is about themselves in their past lives or smth(not revealed yet)
a person on twt did a translation of the hieroglyphics and this Is what we know so far
1. The five siblings had horus as well as sixth sibling ( we call him horus the elder)
2. He n Seth had something going on (some theories suggest romantic involvement since there is a mention of taboo between them
3. For some reasons unexplained this past horus or horus the elder is murdered by Seth who devasted, runs away and is called murderer by isis n comforted by nephythys
4. Fan theories say that Osiris must've done something to make Seth kill horus after which isis must've collected his ashes and planted them in her womb and did magic to make everyone forget their past collectively
That's pretty much everything that's being discussed and I hope I was able to describe it properly
This yandere story is pissing me off. How are you an obsessive lover yet u kept the object of ur affections neglected in a dark room with no food for 4 days because u were "sad". Like what if he died or something. What deepness does this love even hold at that point
Well from my point of view yanderes are extremely selfish. They do things to the person they “love” because that’s what they want. They put themselves before everyone. Which is what Winter is doing.
There are certain subtypes of yandere (in fictional theory) yes your selfish yandere seems more plausible in this one. His actions and words are completely contradictory, author wrote him like he waited so long for his one true love, obsessed over finding him and then forgot him in a dark basement for days on end. It's too weird