When Rachel Bloom and Aline Brosh McKenna came up with the concept for Crazy Ex-Girlfriend, The CW's Golden Globe-winning musical comedy, they envisioned a four-season plan. It would follow Rebecca Bunch (Bloom) from her impetuous move from Manhattan to West Covina in the hopes of winning back her camp boyfriend Josh Chan (Vincent Rodriguez III) through her downward spiral until she hit rock bottom and came out the other side, ready to face herself and take accountability for her actions. And despite the low (but consistent!) ratings, they made it happen. The critically beloved series' fourth and final season kicks off Friday, bringing to fruition Bloom and McKenna's dreams and giving fans a chance to say a proper goodbye to Rebecca Bunch.

"After the first pickup, I was pretty confident [that we'd make it to Season 4]," McKenna tells TV Guide. "Because if you're going to pick up a show with ratings that are that bad, why not do it again the next year when the ratings are identical?"

"We just kind of didn't think about it," adds Bloom. "We had to live as if we were doing it because there was no alternative."

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So what can fans expect of Crazy Ex-Girlfriend's swan song? Bloom and McKenna share seven things to know about the last 18 episodes, including the fallout from Rebecca's guilty plea, the anticipated return of Greg and why Rebecca's happy ending won't necessarily involve riding off into the sunset with one of her many beaus.

Donna Lynne Champlin and Rachel Bloom, Crazy Ex-Girlfriend Photo: Robert Voets/The CW

1. Rebecca REALLY wants to go to jail. Rebecca was not playing around when she pleaded guilty to attempted manslaughter, and when the season picks up a few minutes after the end of the Season 3 finale, you'll start to understand why. "She is digging into the symbolism," Bloom says. "Her livelihood after her diagnosis is still telling herself stories. So she's telling herself the story of, 'I need to pay penance, I need to be in jail.' And she's grappling with that in the first episode of, 'What does penance look like? What does taking responsibility really look like?'"

Apparently, Rebecca seems to think this looks like going to jail for a crime she didn't commit. Of course, something Rebecca will also have to grapple with is how to give herself a break when things aren't necessarily her fault (like, say, pushing someone off a balcony to stop them from murdering your ex-boyfriend). And while part of this journey will take Rebecca to prison, the fallout from her almost killing Trent won't define the entire final season.

"That's mostly in the first part, but I would say the things that she learns from it and the way she realigns her priorities strings through the whole season," McKenna says.

Rachel Bloom and Santino Fontana, Crazy Ex-Girlfriend Photo: Scott Everett White/The CW

2. Greg is returning, but he'll look a little different. OK, "a little" might have been an understatement — Greg will look a lot different, like a completely different person, when the show returns. Skylar Astin will be taking on the role of a "reimagined Greg," who will return to West Covina toward the middle of the season and stay through the end.

Greg, who was originally played by Santino Fontana until his exit in early Season 2, won't just be changed in appearance though. "You know when you run into an ex and they seem almost like a completely different person? It's a little bit that," McKenna says of what to expect of Greg now. "But it's more for [Rebecca] because of the way she sees the world and the situation that she was in in the first two seasons. So it's really about how they perceive each other, and we have the great luxury of having him have been gone for a while so we can really reimagine and figure out a way to figure out that story with a different character in certain respects."

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"I think the main thing is that Greg and Rebecca's relationship was based on self-hate and a little bit of hatred of each other," adds Bloom. "I think that Greg coming back and being a different person is not only an example of how perception changes in general — especially people we've been with and haven't seen for a long time — but how self-love can change both you and the way you perceive someone."

Skylar Astin Photo: Michael Tran/FilmMagic

3. Greg and Rebecca will still have major sparks. Even though Greg and Rebecca are both in very different places than they were when they were together, the couple's chemistry will reignite this season, with Greg again becoming a point in Rebecca's ever evolving love triangle. "It's definitely going to be confusing for her," Bloom teases.

However, before Greg and Rebecca have any shot of a romantic future together, they have to deal with the fact that Rebecca slept with his dad. While Bloom notes that "it's hard to come back from that," McKenna does make it seem like it isn't necessarily insurmountable.

"There's so much water under the bridge in certain respects. But in other respects, it's like a new relationship," she says.

Scott Michael Foster and Rachel Bloom, Crazy Ex-Girlfriend Photo: Michael Yarish/THE CW

4. Greg won't be the only thing complicating Nathaniel and Rebecca's relationship. One thing the Season 3 finale made abundantly clear is that Nathaniel (Scott Michael Foster) hasn't come nearly as far as Rebecca in terms of his own self-reflection and desire to grow, which will become a huge obstacle standing in the way of any potential romantic reconciliation between them.

"It's a long road with him because he's so behind where Rebecca is. And we're definitely playing with the idea of the reformed asshole and how he hadn't really reformed," Bloom says. "He almost got it, but he took the wrong message from what Rebecca was saying."

Adds McKenna: "I think one of the things that we try very hard to explore on this show is that the love relationships cause people to see themselves, to self-examine, and I think he never connected with anyone as much as he did with her. And so it really is about himself. Love relationships in many ways are like looking in a mirror. And he sees a certain version of himself in her and that's as much as what he's attached to as her. And so as he starts to look within and change, there's sort of inevitable changing in their relationship. But he doesn't have the greatest values."

Rachel Bloom and Michael Hyatt, Crazy Ex-Girlfriend Photo: Scott Everett White/The CW

5. Rebecca will start learning how to manage her diagnosis. Last season saw Rebecca get diagnosed with Borderline Personality Disorder (BPD), something she initially struggled to accept because of the stigma surrounding the diagnosis. Now that Rebecca has come to terms with her BPD, the final season will explore how she learns to manage her mental health, including working through her abandonment issues and habit of "splitting," which is the tendency to see things as either all good or all bad.

"It is about trying to let go of the narratives that she's feeding herself and also embracing the nuance of who she is, which she's been working on and will continue working on," Bloom says.

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"I think we have very good language now for addiction and people understand that once an addict, always an addict and you're always dealing with that," says McKenna. "And with mental health, for some reason, people feel that there's a before and after. There isn't, really. There's just sort of a management. And so Borderline is something you manage, and it's not really mostly done through medication. There's some aspect of it that would be medication, but it's mostly her managing this mental illness, which she will have for the rest of her life in some respects."

Rachel Bloom, Vella Lovell and Donna Lynne Champlin, Crazy Ex-Girlfriend Photo: Scott Everett White/The CW

6. There's a lot of great stuff coming up for Rebecca's friends, too. This season won't be all about Rebecca and her love interests. All of the supporting players will get their due as well.

The final season will explore the future of White Josh (David Hull) and Daryl's (Pete Gardner) relationship now that Daryl has a baby; where Valencia (Gabrielle Ruiz) goes next since she's already found love and a booming career; Josh's continued introspection and desire for self-growth; and Heather's (Vella Lovell) next steps now that she's learned what she wants and how not to quit. But if we're being honest, the friend whose journey we care most about in these next 18 episodes is Paula (Donna Lynne Champlin), whose relationship with Rebecca has been the bedrock of the series since the beginning (even if it has been a bit problematic at times).

"It's funny because people love Paula, but they're always very quick to point out her flaws," McKenna says. "But all the characters on our show has flaws. Everyone we know has flaws, you know? I think there is a thing where people want to see the best friend character as somebody who is almost like a spiritual Sherpa in a way, and Paula is just as messed up as Rebecca in her own ways and her pathologies lines up with Rebecca's in kind of an interesting way. So we always have a lot to play with her because she's not perfect, as is no one. And she has certain challenges — her children are getting older, she's becoming an attorney — so it was enormously fun for me to write."

Scott Michael Foster and Rachel Bloom, Crazy Ex-Girlfriend Photo: Patrick Wymore/The CW

7. Don't necessarily expect the traditional rom-com happy ending. Stories like this often end with the heroine living happily ever after with her one true love, but just because Crazy Ex-Girlfriend plays with rom-com tropes doesn't mean we should prepare for a rosy rom-com ending.

"Dan Savage says something really smart about love, which is: There's no such thing as The One," Bloom says. "This fallacy of fate, The One, you find the 0.999 percent and you round up to one. And so this idea of 'meant to be,' 'ending up with,' it's the question that we're all used to asking with romantic comedies. But it's ultimately not really the question that we're solving."

Crazy Ex-Girlfriend returns for its final season Friday, Oct. 12 at 9/8c on The CW.

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(Disclosure: TV Guide is owned by CBS Interactive, a division of ViacomCBS.)