Complex sentence: The story focuses on Usagi Tsukino, a young girl who is granted the power to become the titular character and is joined by fellow Sailor Guardians in search of Princess Serenity and the Legendary Silver Crystal.
Split into simpler sentences: The story focuses on Usagi Tsukino who is a young girl that is granted the power to become the titular character. Usagi joins her fellow Sailor Guardians in search of Princess Serenity and the Legendary Silver Crystal.