Act 8 - Makoto sees Rei being taken away from the temple and follows her to a hotel. She even assaults the bodyguards outside the door to get in. Rei wasn't in any trouble but when Makoto says she thought she'd been kidnapped, Rei realises that Makoto had come to save her. She doesn't quite know what to make of this, having never had any friends before.
Mako running through the hotel pushing Rei on the service cart. It's probably the most carefree we've ever seen Rei.
Act 10 - Usagi had run away from home due to an argument with her mother. At the end of the episode she barges into the kitchen and immediately flings her arms around her mother. Her mother doesn't bat an eyelid in the slightest and just smiles, knowing that Usagi would have come home eventually. Usagi's brother even asks why she isn't being scolded but the two just ignore him and start making dinner together.
Act 11 - Minako is forced by circumstance to spend the day with Usagi. Initially annoyed by her, Minako eventually has fun she hasn't had before.
Act 16 - Usagi is delighted when Ami starts calling her by her first name at last. And she's even happier when she realises that her friends are referring to Ami by her first name too.
Act 28 - Ami breaks free of Kunzite's brainwashing and the senshi welcome her back.
Act 29 - The girls are celebrating getting Ami back by throwing a party at Crown. Usagi and Ami sing karaoke with Makoto dancing along...and Rei joining in. One of the most adorable moments ever.
Act 34 - Ami spent the day with Rei in Karaoke Crown after both of them ran away from parental resentment. Ami was conflicted between her student and senshi life as she always wants to make her mother happy, while Rei despises her politician father for not being there when Rei's mother died years ago. Ami and Rei's bonding enabled them to reconcile with their parents.
Act 40 - When Minako wants to leave her celebrity status to be a full-time senshi, Rei joins forces with Minako's manager as Mars Reiko to take over Minako's projects. This reignites Minako will and her manager puts on a game show competition. The senshi are glad to represent Minako and Rei and this is the main episode that all five of them (and Luna) bond together in their civilian identities.
On a meta-level, the girls are still connected with each other after the show ended, and they often meet-up when one of them has a birthday or an impromptu reunion despite their schedules. Such photos of their reunions are often seen in Twitter.