*Julia Krystal, known as Masumi Kotsu in the Japanese version, is a character in the Yu-Gi-Oh! ARC-V anime and is the representative for the Leo Institute of Dueling Fusion Summon course.

Masumi means "beauty" and "purity", most likely referring to her affinity of jewels, her father's occupation and her Deck. Her first localized name sounds similar to "jewel", and her English surname is a corruption of "crystal".

Julia is a direct, straightforward and bold individual, showing little to no hesitation in saying what she believes. Due to her father's job and witnessing and appraising the value of jewels, she is seemingly capable of detecting talent and hesitation within people, as she did with Zuzu at the start of their Duel. Although Julia shows a penchant for mockery, most of what she states is accurate thus, she does not act out of plain arrogance but on observation. She was not easily fooled, as seen when LID Elites lied about Professor Marco being hurt in his Duel, and she was thus willing to seek the truth. Despite her bold exterior, she was visibly unnerved during her first meeting with Shay and when she saw the gouges that his monster had left in an overhanging road.

Julia is also a caring person, valuing her friends and her teachers, and after Professor Marco's disappearance, she became frantic in her attempts to find him. She cares for (and possibly has a crush on) Marco particularly, and doesn't tolerate insults towards him.

After Z-ARC's defeat and the Standard Dimension being reborn into the "Pendulum Dimension", Julia had lost her memories of Zuzu and the events involving people from other dimensions. She was present during the Battle Royal with Dipper and Kit. She was later seen watching Yuya's Duel against Jack Atlas with Dipper and Kit and applauded when Yuya won. She then watched Yuya and Declan's Action Duel. She was happy when Yuya won the Duel and witnessed Zuzu's revival.

Julia uses a "Gem-Knight" Deck, which focuses on Fusion Summoning, spearheaded by her ace monster, "Gem-Knight Master Diamond", which is later replaced by "Gem-Knight Lady Brilliant Diamond". She chose to use a Gem-Knight Deck because of her father’s occupation as a jeweler. She usually attempts to perform an OTK with "Master Diamond" by copying the effect of "Gem-Knight Topaz" or "Gem-Knight Lady Lapis Lazuli", which along with "Brilliant Spark", can inflict large amounts of damage to her opponent.

She later utilizes cards such as "Brilliant Fusion" and "Crystal Rose" to easily Fusion Summon her "Gem-Knight" Fusion Monsters, and even Summon them with a single material through "Brilliant Diamond", focusing on overwhelming her opponents with an array of strong monsters. She uses Action Cards to mitigate the effect of "Brilliant Fusion" so as to not lose offensive power.*