Peruru is Pegasus/Helios
Peruru not only resembles Helios, but shares his polite mannerisms. He's a child (like apparently Helios with the 30 year old man voice is), but he refers to Rini as a kid, outside of the candy store, as if that's separate from what he is, although they appear to be the same age.
When Rini first meets Peruru, she states his name as if she knows this is something she forgot was important to her. Maybe, subconsciously, she realizes this is Helios from when he was her age, two or three years younger than when she had first met him.
On the beach, Peruru talks about being a dream fairy and that Rini will always be in his dreams, similar to the last moment Helios and Rini share. Peruru/Helios could have started out as a dream fairy and is later promoted.
Peruru senses this eternal connection with Rini, when she kisses him on the cheek, like he can feel they'll be allies again. Then, two or three years later, when Rini's dream light partially frees him, Helios knew how to help the Sailor Scouts, because had already seen their powers assist him.
In the episode (season 4, episode 31) where Helios confides in Rini about what happened to Eleysion, the circus from the dark moon resembles parts of the boat the children were taken on. There are also a few birds around that resemble the ones Peruru's colleagues turned into. So maybe he kept them out of a reluctant love, which is why he doesn't appear to have any family apart from Rini and the others.
Timeline Of Events (both cannon and my own imagination)
-Badiyanu goes around collecting three teenagers and a ten year old boy named Peruru, all victims of abusive homes (Peruru did marvel at how nice all the mothers at the candy store were), to be dream faeries for her. They time travel together. While the four of them believe that Badiyanu strives to keep all the children safe in their dreams, she really wants to destroy the earth. Although her methods are notably intense, she tricks her four agents into continuing to follow her by playing on their longing for a mother-figure.
-Peruru meets up with Rini and the plot of "The Black Dream Hole" occurs. (See the notes from above.) Additionally, I consider the moment when Badiyanu, while she clutches her tightly, makes Rini's clothes disappear to be molestation. It did result in everyone else gasping.
-About two years later (when he started a super-mega puberty that gave him a thirty year old man voice at age twelve), Peruru is back in his right time--the future that Rini visits from. Still desperate for a family, he finally reunites with Rini (who is his age), the Sailor scouts, and meets Darien in Crystal Tokyo that is still in repair from the season 2 villains. Peruru uses his powers to repair Crystal Tokyo and renames it Eleysion.
-Peruru adopts a new name, as a means of starting over. Because of his love for Rini, he chooses Helios, so (subconsciously) metaphorically she is the moon and he is the sun. He has also acquired the power of transforming into a winged horse and Rini suggests he call that form Pegasus. While he and Rini grow closer, Pegasus wonders if Rini reciprocates his feelings, since she only kissed him on the cheek in "The black dream hole" and he doesn't know if that was romantic of platonic. Rini and the others decide to not tell Helios about his involvement in the season 4 adventure, so they don't mess with the time-line.
-Nehelenia breaks free and ends up in Eleysion. She gathers followers to attack Sailor Moon and the others in an act of revenge because Queen Serenity (Sailor Moon's mom) imprisoned her. She is not aware of Helios's presence and he is not yet aware of who she is, but, through a ripple in the universe caused by her attack, he ends up in whatever year Queen Serenity was alive in. She instantly trusts him, because of a connection she senses.
-To preserve the time-line, Queen Serenity hides Helios on earth (and is his only visitor) to protect the golden crystal for her. While Pegasus hasn't been informed of how Queen Serenity died, he reveals that she is not in her daughter's and granddaughter's future. Queen Serenity is deeply pained by this, but stays strong because she has faith that her absence is for a good cause and she is sure that her daughter and granddaughter have good friends, advisers, a husband (for Serena), and an aspiring husband (for Rini) to be their allies. Helios is embarrassed that she can detect his love for Rini, but she assures him that she believes, if he feels this strongly for her granddaughter(Queen serenity figured out why he named himself Helios), then Rini does reciprocate his feelings. Queen Serenity also adds that she couldn't imagine anyone else nice enough to marry her granddaughter.
-The events from the flashback in (Season 4) episode 36 occur. Queen Serenity is deeply ashamed about what has happened to Helios and dies before she can tell Luna and Artemis about his imprisonment. Since Helios doesn't appear to have clothes on, when he is imprisoned by a woman who wants his heart, I can only assume that Nehelenia wanted to hurt him the same way I think Badiyanu hurt Rini.
-During season 4, Helios realizes Rini does love him (in the past and future) and that she and the others didn't tell him about all of this to preserve the time-line. He also thinks that is best for him too, but does reveal to Darien (because he gets a chance) that he knows all of them in the future (he also lets it slip to Rini a few times when he says Eleysion is where they live). Darien tells Serena about this and they both decide to keep it a secret, but agree that Serena should comfort Rini by assuring her that they'll see each other again.
-When Helios returns to the future, Rini runs up and kisses him. They both have a tearful apology over the secrets they kept to preserve the time-line. Helios also informs everyone about his adventures with Queen Serenity, which leads to a group hug and a declaration of friendship/love.