The Wizard of The Planets and the Silver Senshi part 1: Harry's new family. When Harry was little more than three the Grunnings drilling company That Vernon works at was bought by a Japanese business firm so they are forced to move to Jubaan Japan. After moving to Japan Harry's abuse by the hands of the Dursley's was exposed to his school teachers. After this happens Harry is adopted by the Tsukino family and is raised along Usagi as her brother. However when Albus Dumbledore finds out about Harry's adoption by the Tsukino's after his abuse at the hands of the Dursley's he goes to Japan and reveals Harry's heritage to the adult Tsukino's and proof of the Wizarding World and asks that they raise him to the best of their ability. If I were you I would take some inspiration from another Sailor Moon and Harry Potter crossover called The Little Love of Venus and a Sailor Moon and Naruto crossover called Naruto: The Lunar Knight for this part of the story just for inspiration. Now on the topic of Dumbledore I would take a look at Quartermass's Cetra Heritage Saga on his character and see how Dumbledore is portrayed as I am tired of character bashing.

The Wizard of the Planets and the Silver Senshi part 2: Harry's powers and adventures. Now if you follow when the Harry Potter Movies came out Harry was born on 1991 and seeing as the Sailor Moon series takes place in the 2000s to my knowledge so this would make sense to have the worlds merged. Now as Harry develops and goes on his adventures throughout the original Harry Potter Hogwarts books he develops and gains all of his cannon skills, equipment and abilities. Including all the Deathly Hallows for the final Battle against Voldemort and Chaos. However when we get to the start of Sailor Moon Harry does get his own Senshi powers and his own crystal which should be born of the Earth's Golden crystal, Harry's magic, and the scouts own powers symbolizing Harry's earthly heritage, his bond with his friends and family and his growth as he goes down the Sailor Moon Anime(whether its the original anime or The Sailor Moon Crystal reboot is up to you)with his sister and the Inner Scouts and hold his own with them and is their equal in terms of power and is their better in terms of versatility. Also when the gang find's out about the Horcrux in Harry's scar, they eventually exorcise it without killing him but Harry does get the skills and powers Voldemort had as Tom Riddle. Also on the topic of Harry and the Scouts he has to have no Sailor suit or be gender bent, dear goodness no!

The Wizard of The Planets and The Silver Senshi part 3: Parings for the Main protagonists. Seeing as love plays a massive role in the Harry Potter mythos and as Sailor Moon is a love story their has to be love and parings. Usagi has to get with Mamoru, Harry gets with Makoto, Ryo Urawa gets with Ami Mizuno, Minako Aino get's with Viktor Crom, Rei get's with Yuuichirou Kumada, Hermione gets with Ron Weasley. Luna and Artemis get together(the moon cats),and Luna Lovegood get's with Neville Longbottom. For the rest of the casts parings you can do what you want so long as it fits their cannon characters.

The Wizard of The Planets and The Silver Senshi Part 4: The Senshi's abilities. The Senshi gain all of their cannon powers, gear, and abilities throughout the Anime and Manga but they also gain access to Wizardry and learn all spells and powers that Harry can do during his time at Hogwarts. Also Tuxedo Mask gains the Golden Crystal and all the powers he has in the manga but also Wizardry like the rest of the Senshi so he is not given the punching bag treatment like in the Original Anime. You can also give the Senshi Japanese, Chinese, Western Magic and other Oriental styles of Magic and other powers of so long as those powers suit their cannon characters.

The Wizard of The Planets and The Silver Senshi Part 5: Harry's enemies. Every great hero need's great villains so Harry's enemies have to be no push overs and Voldemort has to be Harry's greatest enemy in terms of a personal level and in terms of strength and skill. The Death Eaters have to obtain the powers of Dark Celestial Threats and Youma along with all their cannon powers when they find out how powerful Harry is becoming and the strength of his allies, they have to be legitimate threats. Also Harry has to face the same enemies that the Scouts face in the Anime and Manga and face a mixture of both the main enemies of his series and the Sailor Moon series.

The Wizard of The Planets and The Silver Senshi Part 6: The Neo Silver Millennium. When Harry and his friends get to know their future and what the Neo Silver Millennium holds, it is truly something beautiful. The Wizards no longer have to live in hiding and both sides are working together to build a world where science and magic coexist in harmony and to build a better world. The Neo Silver Millennium also encompasses the entire Solar System and they are able to colonize and terraform all the planets of the Solar System. The Wizarding World's Fantastic Beasts and all of the creatures of mythology are also able to roam free and have wildlife preserves and all of earth's ecosystems are revitalized and repaired.

The Wizard of The Planets and The Silver Senshi Part 7: Harry Potter's allies. When Ron, Neville, Hermione, and Luna Lovegood encounter the scouts, they not only gain their own crystals but they also gain the powers of Endymion's four generals as they were before they became Youma but also their Youma powers but purified and added to their new crystals along with their cannon powers. This needs to happen so they are not left in the dust or become irrelevant in terms of the story. Also all the Celestial Soldiers in the Manga that are allies to the Scouts show up as well to aid the Scouts and Harry in the Final Battle against Chaos and Voldemort.