This guide mainly focuses on the affinity system in Rebirth, which has the following effects:

Gold Saucer date - The character who accompanies Cloud in the Gold Saucer date scenes during chapters 8 and 12 is determined by the highest affinity. Characters such as Tifa, Aerith, Barret, Red XIII, Yuffie, Cait Sith, Vincent Valentine, and Cid Highwind have specific conditions based on their affinity levels which can lead to different interactions during these scenes.

Dialogue Changes - Throughout the game, Cloud's dialogue and interactions can vary depending on the affinity levels with other characters. For example, how Cloud responds and behaves during significant events or even regular interactions can change, making him appear more interested or disinterested based on the accumulated affinity points​.

Impact on Cutscenes - Affinity levels influence certain cutscenes, such as combo attacks in battles or specific character interactions during key story moments. For instance, in the Ancient Temple dragon boss fight, the characters participating in the final attack can change depending on who has the highest affinity with Cloud.

How affinity is affected:

Dialogue choices you make in response to several conversations throughout the game.

Side Quests usually give a bonus affinity for certain characters when completed.

Using a new synergy ability for the first time with each character awards 1 point for that character.

Certain other choices that will be covered.

Chapter Select and Replayability - After completing the game, players can use Chapter Select to revisit key chapters to explore different affinity outcomes without having to replay the entire game. This feature allows for easier manipulation of affinity points to see various character interactions and endings​

Once you step out into the village, four partner affection dialogues are available.

DIALOGUES
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Aerith
Across the small river in town, standing in front of the book store.

"Wanna climb the clock tower together?"

• "Sure. Let's." ***
  
• "... If I have to." **
  
• "I'm busy." *

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Tifa
Near the big tank in the center of town.

"This tank remind you of anything?"

• "The place I made that promise to you." ***
  
• "The water tower in Nibelheim." **
  
• "Any other mako tank." *

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Barret
In a bar near the center of town, look for dark steps leading down.

"Not gonna have a drop till Seventh Heaven's back up and runnin'."
"First one's on me." ***
"First one'll taste good." **
"No time soon then." *
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Red XIII
Near the entrance to the town. At the stairs.

"One can never be too careful with Shinra."
"I knew I could count on you." ***
"Good boy." *
"Thanks."
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OTHER:
Complete all optional objectives in side quests to increase affinity with party members more. For the "Flowers on the Hill" quests, pick Red Gerberas, Yellow Calendulas, and White Daisies for the maximum reward.

After a boss fight you'll go to stay at the local inn, there are four affinity dialogues here.

DIALOGUES
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Aerith
Inside her room at the Inn in Sea Dragon Square.

"Do you remember the first time we met?"

• "You shoved a flower at me." ***
  
• "The church, right?"
  
• "Nope."

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Tifa
Inside her room at the Inn in Sea Dragon Square.

"Do you remember a guy named Emilio?"

• "Only person from the village I remember is you." ***
  
• "The general store kid?" **
  
• "No. Sorry."

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Barret
Inside his room at the Inn in Sea Dragon Square.

"What do you think Yuffie wants with us?"

• "Your autograph." ***
  
• "To join Avalanche." **
  
• "Those Shinra bounties."

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Red
Inside his room at the Inn in Sea Dragon Square.

"I doubt I'll smell Shinra till it's too late."

"Huh. Not good." ***
"We'll manage."
"Don't worry, never thought you could."
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OTHER

In the Dreaming Of Blue Skies Quest, you have the option of choosing Bovine Meat or Monster Flesh. The Bovine Meat will give the better outcome.

The Parade
Later in CH.4 there is a parade you must perform in. You get an affection bonus for Tifa and Aerith if you do it well. In order to have the best performance you must find all of the troops for your formations. (If you don't want the date with Tifa or Aerith, perform poorly) Here are their locations:

• Follow Rude into the Glabrescent Bar - and though you can’t get served (No Scalp, No Service!) you’ll find soldiers to recruit inside.
  
• Enter the Le Sourire Club to find some upstairs. Check out the jazz band playing a cover of FF7’s iconic track ‘Crazy Motorcycle’, too!
  
• On an upstairs floor of the Barracks building, you’ll find a group being interviewed for TV. Interrupt the interview.
  
• On the top floor of the Barracks there’s another group of soldiers.
  
• In the basement of the Garrison there’s another unit hanging out.
  
• On the main street there’s a group taking a photo with a Rufus cut-out. Snap a nice photo for them and you’ll get a Rufus Cut Out to keep, which is a collectible for a later side activity.
  
• On the same street, a group of soldiers are admiring the cannon.
  
• Head into Cecelia’s Item Shop to find a group perusing its wares. This shop doesn’t have anything new.
  
• In the equipment shop, head downstairs to find another unit.
  
• Finally, recruit the group hanging out in the Accessory Shop.

Arrange you formation like this:

• Grenadiers
  
• Grenadiers
  
• Riot Troopers
  
• Riot Troopers
  
• Flametroopers

This parade formation will result in a showing that can win the event. It has the Ramuh Formation as its first performance, the Shiva Formation as its second, and the Bahamut Formation as its third.

OTHER:
The only affinity choice in this chapter is winning the final round of the Queens blood tournament against Red XIII for a boost to his affinity.

DIALOGUES:

Before Boss Fight On The Beach
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Yuffie:
Eating ice cream near a truck in the middle of the town.

“You’re obviously captivated by my bodacious beach bod.”

• Yeah. Obviously. ***
  
• C'mon, can't you take a hint? *
  
• Nope.

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After Boss Fight On The Beach
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Aerith
“I start thinking things so dark and ugly that it scares me.”

• They’re just thoughts. ***
  
• Everybody's got someone they hate. **
  
• Then don't think. *

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Red
"I know I should strive to maintain my composure around him, but..."

• Don’t sweat it. ***
  
• We had no choice.
  
• Yeah, you should.

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Tifa
“Feels like it’s been ages since Seventh Heaven.”

• Lot’s happened since then. ***
  
• Wanna go back?
  
• It hasn't been that long.

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Barret
“I couldn’t do a damn thing for those poor bastards.”

• You tried. That’s all you can do. ***
  
• This is on Hojo. **
  
• Can't save everyone.

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OTHER:
In the Rendezvous Quest, (Shell finding date with Aerith) give the Gigantopod Shell to gain affinity with Aerith.

Recruiting Yuffie
Later in the chapter Yuffie offers to join the party.
To get the most affinity, you can't seem too eager to recruit her. Choose these options:
1."Beat It."
2. "Kinda."
3. "Hardly."
4. "You can come with."

Choosing beach attire:
Matching clouds outfit to either of the girls gives bonus affinity.

Cloud's Ocean Chocobo outfit pairs with Tifa's Majestic Glamour and Aerith's Floral Delight.
Cloud's Wild Surf outfit matches Tifa's Shining Spirit and Aerith's Pink Mermaid.

Boss fight:
Immediately before a boss fight on the beach you can choose which group to help.
Help Aerith & Barret gains affection with Aerith & Barret.
Help Tifa & Red XIII gains affection with Tifa & Red.

OTHER:
Later in the chapter you make a choice on which minecart track to use.
Barret will prefer the left path, on the upper track.
Yuffie will prefer the safer track on the right-hand side.

The affinity gained here is a combination of whose route you chose and how well you do in the mini-game on that route. Affinity can be gained for both, but more for whoever route is chosen.

Other:
Early in Chapter 8, you'll face off with Dio in the 3D Brawler mini game. Beating Dio gives affinity for Red.

At the end of Chapter 8, you'll play a mini game where you fire Barret's gun at enemies from the back of a Buggy. Doing well gives affinity for Barret.

After the scene with the group at the monument on the hill, Red will be off to the side of it. He will ask you to identify Gongaga Mushrooms. Pick the patch to the far right to gain affinity with Red.

DIALOGUE
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Barret
West side of town, near Cissnei's house.

“Wonder what kinda stuff we’d end up growin’.”

• Mushrooms ***
  
• Black milly? Red shelly?
  
• Onions.

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Aerith
The east side of town.
“Pretty selfish, huh? Waltzing in there, stirring up memories…”

• They didn’t seem to mind. ***
  
• You're too hard on yourself. **
  
• You mighta crossed the line.

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Tifa
North side of town, near mushrooms.

“What sorta thing would you go for?”

• Gonna go with the pot roast. ***
  
• Pilat, I guess. **
  
• Soup's good.

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Yuffie
Yuffie is on the couch inside of Cissnei's house.

“I am so, so bored…Bored right out of my brain”

• Nice song. Funny too. ***
  
• I'd love an encore. **
  
• Quiet down, will ya?

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DIALOGUES:
Later in the chapter you'll attend a bonfire ceremony, the party can be talked to here.
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Red
“Just forget I said anything.”

• I’ll lend an ear. ***
  
• Don't gimme that bull$#%&.
  
• Wasn't listening.

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Barret
“So what - we sit here and ‘theorize’?"

• No, we fight. ***
  
• Maybe you'll learn something.
  
• What do you wanna do?

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Tifa
“Did I sound as awkward as I felt?”

• You did good. ***
  
• I felt for you.
  
• Just gotta laugh it off.

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Yuffie
“Once you die, that’s that.”

• Pretty much. ***
  
• Why do you think that?
  
• Yeah, I totally agree...

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Aerith
What will you do?

• Encourage her. ***
  
• Smile at her.
  
• Stop her.

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DIALOGUES:
Early in the chapter after arriving to the town, there are some dialogues.
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Yuffie
At the northern exit of town.

“What about, say, oh…materia.”

• Yup. ***
  
• Come to think of it... nope.
  
• Dunno.

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Red
At the northern exit of town, close to Yuffie.

“No one wants to hear people badmouth their hometown.”

• This isn’t my hometown. ***
  
• I never liked that place either.
  
• Yeah. Does kinda make you feel like $%&#.

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Aerith
Near the water tower in the center of town.

“You never came up here hopin’ she’d wave?”

• Sounds like something I’d do. ***
  
• What? No way.
  
• That's not funny.

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Tifa
Second floor of her house.

“It was taking a toll…Then you turned up.”.

• Have I helped you get through it at all? ***
  
• Like it was fate.
  
• I never knew that.

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Barret
Barret is in the Inn.

“We gotta do something, right?”

• Hell yeah you’re right. Screw them. ***
  
• I wanna know why they put the robes here.
  
• Not much we can do.

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OTHER:
There are three events that affect affinity.

Beating Yuffie at the 3D Brawler mini-game in Wonderment square gives bonus affinity with her.

Beating Red at a Queens Blood rematch gives bonus affinity with him. He will be in Wonderment square, but only after finding Dio, and before resting at the Hotel (Beginning the Date sequence).

Loveless Play
The role of Rosa will be whoever visits your room first. You need high affinity with female party members if you want one of them to play Rosa, (Blue or higher, checked with L1). If a male party member visits first, Rosa is played by Aerith. If you have no high affinity with anyone, Cait Sith will visit first.
You can make a few errors in the mini-game and still get an S - Rank.
Depending on your performance and character choices, you gain affinity with those characters.

I sort of rushed to get this out and help people who are invested in the dialogue choices. Please let me know any mistakes, missed content, suggestions etc.