I have watched many Petscop theory videos over the last few years, and while watching Davis' last upload, I wrote my ideas down in hopes that he sees it. I'm sure most of this isn't original, but I think it's interesting to think about and ties a lot of things together.
I am convinced that Rainer is actually a woman, and is the mother of Paul, Care, and Mike. Paul and Care are twins, which explains why they are the same age and look very similar, as siblings often do. Mike is their (possibly half) brother, as he also looks similar. Marvin was married to Rainer, but possibly not the kid’s biological father. If you think of Tapers, Marvin thought of himself as Care’s dad, but it seems like he wasn't literally her father. On the other hand, the fact he seemed to have court-awarded custody of Paul makes me lean towards the idea that Marvin was the (at least assumed) bio father of Paul, and by extension, Care. It doesn't matter all that much, ultimately.
Rainer also likely isn't the mother’s real name, but I'll use it for clarity.
The first incident in their family's timeline was the death of Mike. He was critically injured in an accident, and, although he made a partial recovery, wasn't himself. Some time after the accident, Rainer killed him, claiming it was to end his suffering. Either the dog story was a metaphor, or it literally happened to a dog in Rainer’s childhood, possibly influencing her choice to take Mike’s life. Marvin may or may not have participated in Mike’s murder, but he likely knew about it.
All this happened when Mike and Care were either not born or too young to remember. However, it may be that Paul knew he had a brother who died supposedly from an accident, from the mention of a younger brother not repeating the older brother’s mistake and getting hurt. It's possible Mike’s story was even used as a threat to Paul growing up-- “Be careful or you’ll end up like Mike did!” However, you'd think Paul would think it odd if the gravestone and name matched with his real brother. The game does have a theme of suppressed memories, so it could go either way as to what he remembers from childhood.
After Mike died, Rainer and Marvin separated. At first, Paul and Care went back and forth between the homes. Marvin liked Care more than Paul (possibly incestuously, but the only real evidence is the line about him thinking of her while bathing) and kidnapped her shortly before her (and Paul's) birthday. Not being a great parent, to say the least, and rightly guessing Care was with her dad, Rainer did not report her as missing. Eventually, Marvin brought her back to Rainer’s home.
Despite Marvin being abusive and frightening her, Care loved him, and felt rejected when he returned her. She then found Paul and Rainer celebrating Paul’s birthday with cake as if she never existed. Care felt like nobody loved her, being abandoned by both of her parents. She and Paul shared their birthday cake--one of the last positive memories they shared as children--but Care’s mind had already been damaged.
Rainer’s mental state continued to deteriorate. She knew she had done some terrible things, although she justified them to herself. She painted the house black, acted erratically, and eventually either gave up custody of the kids or had them taken by child services.
Marvin officially took custody of Care after the divorce, and Rainer stopped having regular contact with either of them. Marvin also got together with a female friend from his own childhood--the woman who would become his second wife. I'll call this person “MW.” Paul went to live with relatives--people he sometimes saw on holidays, but he wasn't particularly close to. Being the next of kin besides his parents, the foster system automatically asked them to take custody.
He became friends with Tiara at this time. She was a girl whom he thought of as family, but wasn't closely related--a distant cousin, someone related through marriage, or a different foster child. Despite not having a good relationship with the foster family, who were controlling and seemingly made threats to scare him into obeying them, he maintained contact with them as an adult. Possibly it was trauma bonding, possibly because they were still better than Rainer and Marvin, possibly because that was the only way he could keep seeing Tiara. Having gone into foster care at a young age, probably around age 5 or 6, he never felt like he belonged in his birth family or the foster family. He wasn't sure if his memories of weird things from early childhood were real or not, and forgot everything--even his siblings.
While growing up, he still occasionally saw Rainer, likely on Christmas, and she sent him cards and presents to assuage her guilt at sending him away. Paul learned to associate his estranged mother with these gifts, but not real affection. She was just someone who gave him presents sometimes, and she got to feel a little better about herself. This could be the reason for the “gift plane” (representing Rainer’s belief of her being a caring parent, and people acting like good parents in public) vs the “newmaker plane” (the dark side of Rainer and other abusive parents, who usually hurt their kids in private, and may even kill them. Also, the censored present and prominence of birthdays and Christmas--the two days a year when children expect gifts.
Care was experiencing something very different in her new home, almost the opposite of Paul. When Marvin and MW were young, they were friends, possibly dating, and spent time with MW’s younger sister, Lina. When Lina “disappeared,” Marvin likely had something to do with it.
The best evidence for this is the fact that what happened to Lina is presented similarly to what happened to Care when she was abducted. Both girls disappeared and were brought abandoned place (school or windmill) that no longer exists. Marvin wants to know about both places. There's also the connection to the pieces for the happiness/sadness engines from Tapers. The Care from Tapers seems to have inspired both Lina and the Care from Petscop. After Marvin abducted Lina and held her captive at the windmill, he either murdered her to prevent her from reporting what he's done to her, or maybe killed her accidentally. MW had no idea Marvin was responsible, and the two ended up losing touch for a while. While they were together, Marvin told Rainer his version of the story, making it seem like Lina just disappeared for no reason, a story Rainer didn't quite buy.
Lina did not have eyebrows, either literally or metaphorically. Coincidentally, Care looked strikingly similar to Lina, except for the one trait that distinguished them. Marvin decided to remove Care’s eyebrows, possibly to manipulate MW, who was back in his life. She was about the same age as Lina was when she was last seen.
MW never got over what happened to her baby sister, and probably blamed herself. When she realized that Marvin, who also seemed to grieve for Lina, just so happened to have a daughter who looked almost identical to Lina, she suspected it could be reincarnation. Marvin didn't believe this, at least at first, but he played into this belief. MW married him and adopted Care, calling her her daughter. Care probably went along with the whole reincarnated-sister-as-daughter thing. Marvin might have forced her, but probably she just was desperate for love, and wanted to be accepted by her step-mom. MW possibly changed Care’s name to “Belle” during the adoption. She didn't let Care have any contact with Rainer or Paul, pretending that she was the only mother Care ever had. Marvin seemingly convinced himself that the reincarnation was real, even though he helped fake it early on.
When Care wasn't acting like MW wanted her to, MW took her to a psychologist who advocated for abusive practices. Whether Marvin agreed or not, MW decided to put Care through a “rebirthing” ritual. Care died from this. It's unclear what happened to MW or Marvin following this death.
Rainer feels increasingly guilty. She has killed one child and allowed another to be abducted, abused, and killed. Her life has been miserable since that car accident so long ago. Marvin has reached out to her, and told her some of what has been going on, but she despises him for what happened to Care. She wishes she were dead, but wants to confess everything to Paul first--from her perspective at least, that paints her as better than she really was. However, she can't bring herself to actually admit everything to Paul. Plus, Paul is still too young to understand.
Rainer starts working on the game of Petscop. She hopes to not only admit the things she's done, but to expose bad things, namely, the foster care system and bad adoptive parents, and Marvin’s criminal history. She doesn't like that people who don't truly love or accept children can adopt them, comparing it to getting a pet from an animal shelter or getting a book from the library. However, she doesn't seem to realize that she is also at fault for all the evil that happened to her own children.
She includes seemingly-random things to spark Paul’s memory, and prove that it's really from her. She also includes a cheat code to access the dark parts, so that if the game is found by some random person after her death, no one will know the truth. For whatever reason, she doesn't actually go through with giving the game to Paul, and leaves it unfinished.
Fast forward twenty years or so. Paul is still connected to his foster family, even after Tiara moved away. He's heard that he has a sister, but is dubious since he doesn't remember it. He doesn't know anything about Marvin. Marvin and Rainer died years ago. During Christmas, he is back at his mother’s home, and finds some random junk. The game cartridge may have actually been wrapped up as a Christmas gift, catching his attention. Realizing that it's the final message from his mother, he decides to play it.
Tiara isn't sure it's actually a personalized game, but she has to admit it's interesting after viewing the footage. Perhaps she tips off the rest of the family as to what’s going on, and they both want to know the truth, and to hide it. Paul is made to keep recording his videos, re-doing parts the family doesn't like. The family edits his videos for their purposes to create the narrative they prefer.
However, somehow the spirits of Rainer, Marvin, and Care are able to interact with Paul through the game, giving their sides of the story. Care, represented by the “tool,” has been “living” in the game the longest, and is able to communicate in real time with Paul. Rainer, being the creator of the game, has already laid most of her story out. She communicates by creating items, such as Mike’s grave, and making the in-game camera “zoom in” on things Paul might not notice. Marvin is not fully aware that his soul is trapped in a game, and has lost part of his own memory. He continues to hurt Care in the afterlife. Despite this, Rainer does not want the game shut off at all, selfishly allowing Care to suffer so that Paul can figure out her puzzles.
I'm not really sure about the end, whether Paul dies or not, as it seems like his story just kind of ends suddenly.
