Ryo Urawa is a boy who has a mysterious power to see the future.  He uses this power to get perfect scores on school tests in an effort to show he is as smart as Ami Mizuno, who he is infatuated with.  But then he becomes ashamed of this cheating.

He makes several attempts to admit this to Usagi & attempt to correct it, but before he can successfully do so, Zoisite uses his Black Crystal to turn him into Bunbo, one of the seven Rainbow Crystal monsters, and get the yellow Rainbow Crystal that is inside of him.  Though remembering something Mercury had just told him, Bunbo attacks Zoisite instead, causing the yellow Rainbow Crystal to switch to the senshis' possession.  So Zoisite uses his Black Crystal again to make Bunbo stronger and cause it only to fight the senshi.  But the senshi eventually prevail, restoring Bunbo to Ryo Urawa.

Picture of Bunbo, from WikiMoon

A short time later, Ryo has to transfer schools again because of his dad's work.  It is at this point that Ami finally shows she likes him (though she would never admit this).

He first appears behind Ami Mizuno as she's walking down a sidewalk absorbed in a book.  He greets her, which prevents her from getting injured (if not worse) by a heavy metal beam being used at a construction site that was about to fall.

A little later, many students are gathered around the posted results of a midterm exam.  His name is at # 1 on the list, while Ami's name is at # 2, one point behind him.  So Ami flags him down to congratulate him as he was about to pass by, and once he saw who it was, Ryo Urawa runs away, embarrassed.

A little later that school day, Usagi Tsukino finds him up on the roof of the school, looking at a newspaper clipping.  When Usagi notices that the clipping is of an article from where Ami had been best in the nation at a (nation-wide) mock summer exam, and included a black-and-white picture of Ami, she teases him about liking Ami.  He quickly denies it, giving the excuse that he just wanted to study hard to be like Ami ever since noticing that newspaper article.  Usagi then congratulates him for surpassing his goal, and he denies that also, giving the excuse that he just happened to be right about what was on the tests, and saying Ami is far more gifted than he is.  He soon stops himself, apparently because he's starting to blabber his true feelings for Ami, and looks down from the roof on her playing ball with a couple classmates.  When Usagi notices him looking down at Ami there, she suspects something more, and promises to help him as she runs away.  He then stops Usagi to warn her to be careful around water, and right afterward, a construction worker splashes her with the water he threw out of a bucket.  As the worker approaches Usagi to apologize, Ryo Urawa mutters to himself in disappointment that he was too late.

After school that day, Ryo Urawa and Usagi are on opposite sides of the same table at the Café Bear.  She presents him with a 'gift' in a small envelope, and he opens it to find a color picture of Ami about to bite into a hamburger.  When he thanks her for it, Luna (who was hidden from him on Usagi's seat) notices a 'light' on the Crescent Moon Wand in her bag is blinking, so she quietly mutters that he might be the carrier of a Rainbow Crystal.  Usagi then asks him when he's going to tell Ami that he likes her, to which he replies that when he learned he would be transferred to this school, he made up his mind that he would tell Ami as soon as he did as well as her.  So Usagi promises to bring Ami to him after her cram school that evening and quickly leaves the café.

Outside Ami's cram school that evening, Luna starts to tell Usagi something, but is interrupted by Usagi noticing the cram school is getting out.  Usagi quickly finds Ami and, only telling her that she wants Ami to follow her, quickly drags Ami away.

Meanwhile, Ryo Urawa is walking down another sidewalk feeling down.  Hearing a quiet laugh, he looks at its source to find Zoisite.  He exclaims that the older man is Zoisite, to which the Shittenou member demands an explanation of how he knew his name.  Ryo Urawa explains that ever since he was a kid, he had had the power to predict the future, and that it had been getting stronger the last few days.  He continues by stating that, through this power, he also knows who he 'is', and mutters that it's an identity he never wanted to know about.  Zoisite then smiles and demands that the junior high boy turn into one of the greatest monsters.  But Ryo Urawa outright refuses, exclaiming that he'd rather die than turn into a pawn for the Devil!   So Zoisite uses one of his powers to knock Ryo Urawa a few meters back and onto the ground; he then gets out his Black Crystal to force this change.

Just then, Usagi drags Ami onto the scene several meters away.  When Ami notices that Zoisite is there, Luna tells the two girls to transform, which they do.  When Zoisite notices the two senshi barging onto the scene, he conceals his Black Crystal, stopping the forced change before it can happen.  Moon then tells Mercury to take the boy somewhere safe, and she obliges.  Moon then purposely blocks Zoisite from interfering.  So Zoisite then distracts Moon with another one of his powers and disappears.

Soon afterward, Mercury is with the passed-out Ryo Urawa next to a lake in a park some distance away.  As she puts her wet handkerchief on his forehead, he starts to wake up.  When Mercury mutters to him that they should be safe there, he thanks "Mizuno-san" for rescuing him.  As he passes out again, she is obviously startled that he knows her name.

Meanwhile, Moon is running around trying to find Mercury (and Ryo Urawa).  This is when Luna finally gets to tell her to use her Crescent Moon Wand, stating that the two will be where it responds.  Moon, of course, can't believe this, because it would mean Ryo Urawa is a rainbow crystal monster.  Luna tells her emphatically that he is, which finally convinces Moon to do this.

Back lakeside in the park, Ryo Urawa (still passed out) has a bad 'dream' that he was the monster Zoisite tried to turn him into, and he attacked Mercury.  Mercury then notices the picture of her eating the hamburger that was slightly sticking out of his shirt pocket.  As he wakes up, he mutters that "it happened again", to which Mercury tells him it was just a bad dream.  He then tells her it wasn't just a dream and that he can see the future.  He further explains that he used this "strange power" to get perfect scores on those exams, to which a disbelieving Mercury asks him what he was talking about.  He states he had idolized her, "Mizuno-san", for a long time, but that they were destined to fight each other.  Mercury giggles that he believes that, to which a startled Ryo Urawa exclaims "You don't believe me?!?"  She then states that everything he said was "completely off the mark", and that he was mistaking her for Mizuno-san.  He concedes this point to her, stating "if you say so", but then tells Mercury that if he turns into a monster, he doesn't want her to hesitate at all to kill him!  She responds by telling him "the future is yours to create", that if he gives up, everything would happen like he thought, but that as long as he has faith in himself, he should be able to create any future for himself, closing with a smile at him.

Just them, Zoisite appears over the lake.  Mercury responds by purposely positioning herself between the two males, to which Zoisite states how protective she is, but then wonders out loud whether she would still be that way when she saw the boy's "true form".  Zoisite projects the Black Crystal's power in an arc over Mercury to change Ryo Urawa into Bunbo, "one of the great seven monsters".  But after he turns into Bunbo, and Zoisite successfully grabs his yellow Rainbow Crystal, she mutters "Urawa-kun" while looking into its eyes, which causes him to remember her line "The future is yours to create."  So Bunbo leaps over Mercury, but not before planting one of its sharp claws dangerously close to a now-scared-but-not-flinching Mercury, and tackles Zoisite!  The Shittenou member is so startled by this that he loses his grip on the yellow Rainbow Crystal, and it falls safely into Mercury's waiting hands.  Exclaiming it still has the heart of a human, Zoisite disappears temporarily to escape the tackle-hold, causing Bunbo to fall into the lake, then reappears in nearly the same spot to use the Black Crystal's power to reinforce the message that its opponent is the sailor senshi.  This causes Bunbo to grow much bigger and step out of the lake right toward Mercury.  Scared, she then runs away just as Moon and Luna arrive on the scene.  Still running away from Bunbo, Mercury requests that Moon turn Urawa Ryo back into himself again.  So Moon sends her Moon Healing Escalation attack at Bunbo.  But it doesn't work!  Now with both senshi running away from Bunbo, a still-in-disbelief Moon exclaims the question Why didn't he change back, to which Luna, also running, explains that he was being completely controlled by the evil power now, and that to restore him, she needed to weaken his energy first.  Then Bunbo sent a couple razor attacks at a tree they were running toward, with one of them cutting off a large branch and thus blocking the senshis' path.  Bunbo followed this up by sending another couple razor attacks right at the two senshi.  They successfully ducked it, but that caused the attacks to completely cut off the tree's trunk.

picture of Bunbo, from WikiMoon

Just as Bunbo sent another couple attacks at the two senshi, Mars and Jupiter arrived, sending their Fire Soul and Supreme Thunder attacks to successfully nullify those couple attacks of Bunbo's.  After these two mused that they almost missed their chance to be in the spotlight, Mercury sent her Shabon Spray attack at Bunbo, then told Moon that now was their chance and to help Ryo Urawa.  So Moon sent her Moon Tiara Action attack at Bunbo; when her tiara attached itself to Bunbo's forehead, it successfully weakened, and shrunk, Bunbo.  With Luna urging her to act again, Moon sent her Moon Healing Escalation attack at Bunbo.  With an exclamation of Refresh, Bunbo finally turned back into Ryo Urawa.  When the boy collapsed onto the ground as a result, Mercury ran over to him to help him.  He then woke up and muttered "Mizuno-san" again.

A couple days later, the four senshi girls were at the train station, seeing Ryo Urawa off.  To a question of whether he was transferring again, Ryo Urawa explained that he had to go wherever his dad's work took him, so it couldn't be helped.  Then Ryo started to say something by addressing her as "Mizuno-san", to which Ami told "Ryo-kun" to call her "Ami-chan".  He then gave back the picture of Ami about to bite into a hamburger, stating that he would return for it when he did as well as her on a test.  She accepted it, and Ami then gave Ryo a different color picture for keeps, explaining she liked it better.  As Ryo looked at it in admiration, the train car door closed between him and the senshi girls.  As the train took off, Ami ran down the platform to follow it as far as she could, thinking that he didn't need to worry about grades and that he could come see her anytime.  Then it was revealed that Ryo's new picture of Ami was of her posing with a modest (but cute) smile and in a nice coat and blouse.