We're Still Close Anyway, Mamo-chan
There are a ton of naysayers out there who say that Mamoru and Usagi are only together in present-day because of their pasts as Serenity and Endymion. But in the first arc of Sailormoon R, I feel that statement falls through. Mamoru still teases Usagi and calls her Odango Atama, but this time around, it's different. Mamoru's much quicker to do things like grab Usagi's hand, laugh with her, and be generally more at ease with her. Usagi may remember the past, but at this point Mamoru's memories still haven't returned. The other thing is, this storyline seems to be the most disliked out of all the Sailormoon storylines, one of the main reasons being it does not exist in the manga. I, however, do really like this arc, and I think it deserves a bit more recognition than it usually garners.
Episode 50 - Usagi's Crisis! The Tiara Doesn't Work
This happens to be one of my favorite episodes. A Virtual Reality game theatre has just opened, and apparently from the enormous line it produces, it's really popular. So, Ail and Ann decide it would be a good place to let a Cardian loose and drain everyone's energy. Seijuro and Natsumi (Ail & Ann's civilian/human identities) go into the theatre with Usagi and Mamoru. Of course, jealous rivalry ensues between Usagi and Natsumi over their beloved Mamoru. While both girls make attempts to force themselves onto Mamoru, Natsumi is easily much worse, and Mamoru begins to lose tolerance with her. Considering Mamoru's infinite patience, she must really be getting on his nerves. However, he doesn't mind being with Usagi at all.
Mamoru: I'm sorry, but I'll decline. [Pushes her away] You can't win someone's heart by being so pushy.
Usagi: [Puts her hand on Mamoru's shoulder] I agree completely, Mamoru, you're the man! [Usagi gets frightened by a VR monster and runs off] Ahhhh!
Mamoru: Odango! A girl like you with no sense of direction will just get lost!! [Runs after her. Ann looks rather irritated]
Mamoru: It must be a special talent to be able to miss this many targets. [Zaps them all] Let's go, Odango! [Grabs her arm and runs with her] If I play, I want to get the highest score! [Hits a bunch of targets]
Usagi: [Thinking] This is it! It has to be like this!
Mamoru: [Hits more targets] Okay! Let's go! [Looks back at Usagi and laughs]
Episode 53 - Mamoru and Usagi's Babysitting Adventure
This is a fairly well-loved episode in the way of the Makaiju arc. The episode starts out with a cardian attacking a daycare/preschool, sucking the energy from lots of babies and mothers alike. Usagi, Ami and Mamoru witness this terrible attack. Mamoru calls for an ambulance and the three of them ride in it with one of the mothers who was a victim.
Once at the hospital, the doctors say that the mother will be okay in about three days. Her baby, Manami, went unharmed because she shielded him during the attack. One problem though - Manami's father was away on business so there was no one to take care of the baby. Mamoru then offered to take care of Manami at his place until the mother was well enough again. Usagi self-appoints herself as Mamoru's helper. As it turns out, Mamoru is actually really good with the baby. Their commitment to Manami sort of foreshadows their future as parents of Chibiusa. Only I'd have to wonder how much more of a handful Chibiusa would be as a toddler...They arrive at Mamoru's apartment. Manami starts to cry and Mamoru attempts to make the baby stop. Usagi also joins in; it's a pretty odd-looking scene O_o. Mamoru suddenly tells Usagi that she can leave if she wants.
Mamoru: I'm the one who volunteered for this. I don't want to make trouble for you.
But, Usagi stays anyway. Manami starts crying again, so Usagi goes to make him some warm milk. Milk doesn't seem to be what the baby wants, and keeps on crying. Mamoru remarks that perhaps her diaper is wet. Usagi tells Mamoru that diaper-changing isn't a job for guys and goes to do it herself. She removes Manami's diaper and shreiks.
Usagi: This baby is supposed to be a girl but she has a wee-wee!
Mamoru: Let me see. You dummy, this baby has a girl's name, but he's a boy. Right, Manami?
[After they change his diaper, Manami starts crying again. Mamoru bets that he's hungry this time; he's right. Usagi makes her usual comments...]
Usagi: It's amazing how you can read a baby's mind! Have you ever had a baby of your own before?
Mamoru: Are you kidding?!
Usagi: Gah, of course you haven't! [Thinking] Why am I always asking stupid questions?
Later the next day, Natsumi decides to waltz on over to Mamoru's apartment and offers to help him with the baby. Of course, it's not for the baby's sake, but so Natsumi can try and get closer to Mamoru. Natsumi sees Manami playing with a box of baby wipes and throwing them all over the floor. She lightly scolds the baby and takes him away from the box. Manami starts crying; one of the reasons being Manami doesn't seem to like Natsumi very much. Mamoru calls from the other room and says that his diaper might be wet. She removes the diaper and says, "Hm, it's not wet." Manami thinks, No! She's creepy! and promptly pees in Natsumi's face. She screams and runs into the kitchen to rinse her face.
Mamoru goes to Manami and feeds him the milk. Natsumi comes back in and holds the baby. Manami pees on Natsumi again! She screams and drops the baby; Mamoru promptly catches him. Natsumi screams, "That's IT! I'm leaving!" and storms out. Mamoru weakly calls after her to not go. Just at that moment, Usagi is walking in. She is hurt that Mamoru was letting Natsumi "help" with the baby. Mamoru seems sort of upset by the way Usagi looks at him. (Odd that he would act that way, they're not going out, right? ....
Mamoru: [Grabs her arm] Wait, Odango Atama!
Usagi: Let me go!
Mamoru: She just came here by herself!
Usagi: It's OK, I'm leaving!
Mamoru: Why are you in such a bad mood?
Usagi: I don't like a guy who doesn't understand a girl's feelings!
Mamoru looks rather dejected at this remark and lets Usagi go. The tense moment is halted when Usagi sees Manami standing by himself. "Look! He's walking!" she says. Mamoru turns around, and Manami begins to walk on his own. Usagi and Mamoru hold hands and celebrate, seemingly forgetting about their argument that had just occured. "He did it! He did it!" Suddenly, Ami walks in.
Usagi: Oh, it's not what you think!! Manami --
Mamoru: He walked for the first time! [He doesn't seem at all embarassed by the whole ordeal.]
At the end of the episode, Manami's mother comes to get her son from Mamoru. She thanks them for graciously taking care of her baby while she was in the hospital. Mamoru and Usagi say their goodbyes to Manami.
[They grasp hands] Both: He did it! He did it! He did it!
Different Than The First Season
Mamoru and Usagi still make fun of each other; moreso at the beginning of the R season than the middle or later on. However, this time it's much different. Partly because of the fact that Usagi's memories of the Moon Kingdom and the events of the previous season, but also because they just have a natural magnetism towards each other. Usagi actually hangs out with Mamoru a lot in this season, something extremely rare in the first season. Mamoru's more eager to grab Usagi's hand and be with her in general. They still have the occasional fight but nothing of the magnitude of the first season. I believe that even if Mamoru's memories didn't return at the end of the Makaiju arc, that after a while Usagi and Mamoru would be an item anyway. Their destiny together knows no boundaries.