In the Infinity manga, Sailor Pluto has been reborn as Meioh Setsuna, a university student. While Setsuna is examining Tellu's plant, her energy begins to be drained. Meanwhile, Haruka and Michiru, in separate places, sense that someone close to them, an ally of theirs, is in trouble. Setsuna's Pluto symbol flares, and Haruka and Michiru, their own symbols responding, teleport to her side. From that point on, the three girls are mostly inseparable, having been united as Outer Senshi. The three are dedicated to their mission to protect the galaxy from outside invaders, and they will do whatever it takes to carry that mission out, even at the disapproval of the other Sailor Senshi. In their past lives, the three knew the same loneliness, having lived solitary lives on their own planets; the only thing that gave them strength was the image of their Queen and their Princess. Haruka, Michiru, and Setsuna also appear to be friends, as seen in the Lover of Princess Kaguya side story and in their decision to leave together to raise Hotaru.

In the Sailor Moon S anime, Setsuna introduces herself as an old acquaintance of Haruka and Michiru. It is unclear whether this means that Haruka and Michiru actually knew Setsuna or whether Pluto was referring to their past as fellow Outer Senshi. Uranus and Neptune show no surprise at seeing Pluto, so either interpretation could be correct.

Pluto sides with Uranus and Neptune, often accompanying them in battles and helping them investigate the Death Busters. We only see them interact as friends a few times - in the S movie, the three appear to hang out together, and in one of the SMS episodes, Michiru and Haruka tease Setsuna about her relationship with Chibi-usa. They refer to each other, however, with the -san honorific. Overall, their relationship seems cemented on the fact that they are all Outer Senshi. Towards the end of SMS, Pluto uses her powers to save Uranus and Neptune, thus ending the trio for some time.

Initially, Haruka, Michiru, and Setsuna want to kill Hotaru to prevent her from awakening as Sailor Saturn. In the Infinity manga, the three are more sympathetic to Hotaru than they are in the S anime; they pity Hotaru for what she has been through, though this is probably because manga Hotaru has suffered much more than anime Hotaru. However, in both the manga and the anime, the three do not hesitate to declare that Hotaru must die. Their feelings about Hotaru's death are not personal - their concern is to protect the world.

Following Hotaru's rebirth as a baby, in both the manga and anime, Michiru instantly adopts a maternal role towards Hotaru. In the manga, Neptune is the one who immediately responds to the baby's cries and holds Hotaru in her arms. Neptune, Uranus, and Pluto decide to raise and care for the baby, who has no one else. In the anime, Michiru affectionally holds, feeds, and burps Hotaru, and she wistfully says that it would be nice if she, Hotaru, and Haruka could just stay like that.

In the Dream arc of the manga, Michiru and Setsuna are Hotaru's mothers, while Haruka takes on the role of Hotaru's father. All four live together in a mansion as a family. They are obviously quite happy together, and as evident by their interactions, they feel genuine love for each other. Haruka, Michiru, and Setsuna treat Hotaru like she is their real daughter. Although Haruka, Michiru, and Setsuna do occasionally complain about Hotaru's mischievousness, it's affectionate complaining, and Michiru calls Hotaru their "princess." Haruka, Michiru, and Setsuna all wear promise rings as a symbol of their vow to raise Hotaru.

In the anime, Michiru wishes for Hotaru to live life as a normal girl. In the manga, too, Haruka, Michiru, and Setsuna have this desire. They also wish for all four of them to stay together like they are, as a family living in peace, even though they know their present life is a "dream" from which they will eventually wake. After Neherenia is defeated in the manga, the four continue to live together. Haruka and Michiru attend high school, while Hotaru goes to elementary school; Setsuna works as a nurse at Hotaru's school.

Setsuna, Haruka, and Michiru are reunited in the SailorStars anime, when Pluto, holding baby Hotaru, appears to Haruka and Michiru. The four live together in a house, while Haruka, Michiru, and Setsuna raise Hotaru. Although the anime mirrors some aspects of the manga, there isn't the same sense of family here. The Outer Senshi do appear to be divided into two groups - Haruka and Michiru, and Setsuna and Hotaru - rather than unified as one group of four. This is probably because Hotaru's real father is still alive; Hotaru was not raised for very long by Haruka, Michiru, and Setsuna; Setsuna and Hotaru rarely get any screen time, so their relationships to characters other than Chibi-usa are unfortunately shortchanged; and when it comes to the Outer Senshi, the anime focuses more on Haruka and Michiru's relationship.

After the Neherenia arc of the Stars anime, Hotaru does not appear until the very end of the season. Setsuna occasionally shows up, sometimes on her own and sometimes with Uranus and Neptune. We do not see much interaction between her and Haruka and Michiru, however. Near the end of the series, Haruka and Michiru go off on their own to fight Galaxia; on their way to Galaxia's headquarters, they are joined by Setsuna and Hotaru. The four vow that one of them will remain to defeat Galaxia. Again, though, there is the feeling of unity among soldiers, rather than unity of a family.

Pluto and Saturn are killed by Uranus and Neptune, who are pretending to be evil servants of Galaxia. Although Pluto and Saturn are initially shocked by Uranus and Neptune's apparent betrayal, they sense something about the way Uranus and Neptune are fighting - that Uranus and Neptune are genuine in their attacks. Although this would seem to indicate that Pluto and Saturn believe that Uranus and Neptune have truly betrayed them, it is my opinion, based on their uncharacteristic acceptance of their deaths, that they realize Uranus and Neptune have a plan. This interpretation acknowledges the existence of an understanding and a bond among the Outer Senshi. That bond is further supported by their very last scene in Episode 200, in which there is a genuine sense of camaraderie and ease among the four senshi that, if not quite familial, is still something.