Julia Krystal

Masumi Kotsu is a character in the Yu-Gi-Oh! ARC-V anime and is the representative for the Leo Institute of Dueling Fusion Summon course.

Appearance
Masumi is a teenage girl with dark skin tone, shoulder-length black hair and red eyes. She wears a small blue shirt with her LID badge pinned on it over a cream one-piece long-sleeved shirt and shorts combination with black skin-tight shorts underneath ending above the knee, and blue boots. She carries her Duel Disk in a brown holster resembling that for a firearm.

Etymology
Masumi means "beauty" and "purity", most likely referring to her affinity of jewels, her father's occupation and her Deck.

Personality
Masumi 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 Masumi 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.

Masumi 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.

Pre-Maiami Championship
Masumi, Dipper, and Yaiba Todo were enlisted by Henrietta to Duel members of the You Show Duel School in retaliation for the apparent attack on Silvio. After Dipper was defeated by Yuya Sakaki, Masumi went next, matched up against Zuzu Boyle. Before the Duel, Masumi noted that Zuzu's eyes had no shine to them, much to Zuzu's irritation. She brought out "Gem-Knight Topaz" on her first turn, but took a large amount of damage from Zuzu's "Melodious" monsters. On her next turn, however, reiterating her comments on Zuzu's lack of brilliance, she brought out both "Gem-Knight Crystal" and "Gem-Knight Master Diamond," using the effects of the latter to set up an OTK. Zuzu attempted to use an Action Card to stop the second attack of "Master Diamond," but by accident instead touched a reflection, and Masumi's attack went through, winning her the Duel and putting the score even at 1-1. She commented on Yuya and Zuzu's embrace after the Duel, prompting Zuzu's swift breaking up of the situation. Yaiba went next, Dueling Gong and claiming to be far stronger than "those weaklings," which infuriated Dipper. Masumi admitted that the comment was annoying, but Dipper had lost, after all, prompting an embarrassed Dipper to sulk in the corner. During Yaiba's Duel, Dipper commented that an "X-Saber" Deck was terrifying to face. Masumi asked him if it was because he'd lost that he was admitting that, once again causing Dipper to retreat to the corner in shame. After Yaiba and Gong drew the Duel, Henrietta proposed a tie-breaker Duel between those who had won; Yuya and Masumi. Masumi was ready to Duel, but they were interrupted by Declan.

Upon learning that her Fusion teacher, Marco, had been in an incident, Masumi became frantic about him. Unconvinced by Tio's reassurances that the LID Elites would resolve the issue, she continued pursuing the culprit, arriving at the warehouse where Yuzu, Sora Shiun'in, and the Dark Duelist were. Immediately accusing the Dark Duelist for the attacks, she demanded a Duel from him. However, before the situation could progress any further, he was teleported away by the ability of Zuzu's bracelet, infuriating Masumi and causing her to accuse Yuya, who had just arrived, of being in cahoots. She dashed off after Sora tricked her into thinking he had run past, while pushing Yuya away.

Still upset by her teacher's disappearance, Masumi resolved to lure out the Dark Duelist and ran off, much to Yaiba and Dipper's protests. On her way to the warehouse, she noticed the two marks left by Shay's monster, much to her horror. Once she found Zuzu and Sora, Masumi demanded a Duel from Zuzu, who hesitated to do so. Before they could initiate the Duel, Shun dashed in and pushed Zuzu over, demanding that Masumi Duel him as a member of LID. She identified him as the culprit from this statement, but could not bring herself to Duel him. At that moment, the Dark Duelist, Yuto arrived, surprising her, Zuzu, and Sora. As Yuto squabbled with Shay, Masumi contacted Yaiba and Dipper, telling them that she had found the culprits, and to bring as many men as they could. After Zuzu protested, Masumi watched quietly as Shay mistook Zuzu for Ruri and Yuto knocked him unconscious as a result. Just as Yaiba and Dipper arrived with Yuya in tow, both Yuto and Shay teleported away via Zuzu's bracelet, causing to her remark fully that the culprit had escaped. When men from LID arrived, Masumi ran towards them, apologizing and saying the culprit had gotten away.

She set herself up as bait on purpose to draw out Shay, as did Dipper and Yaiba. Shay approached her during the evening, asking her if she was alone and where Sora and Zuzu were, Masumi claimed that she didn't know (though unbeknownst to her, Zuzu had seen her earlier and pursued her). She asked him what had happened to Marco, but Shay was initially unsure of who she was referring to, only realizing it when she explained that he was a Fusion user. Shay called Marco and everyone from LID weak, telling an insulted Masumi to sate her rage by defeating him. She called in Yaiba and Dipper, explaining that she'd been set up as bait as she knew what Shay looked like. When her friends arrived, Shay took them all on in a Battle Royale, with Masumi going first. Yaiba and Dipper cleared Shay's field and hand with their "X-Saber" Synchro and "Constellar" Xyz Monsters, leaving Masumi to take out his Life Points. She set up a combination of "Gem-Knight Lady Lapis Lazuli" and "Gem-Knight Master Diamond" that would deplete Shay's Life Points through sheer effect damage, but Shay saved himself with his "Raidraptor - Readiness" Trap Card that he'd activated from his Graveyard, also preventing any battle damage on the turn as well. Shay claimed that their Dueling lacked iron determination and a sense of strength, and he drew "Dimension Xyz," using it to call out his "Raidraptor - Rise Falcon," which gained the combined ATK of all of the trio's Special Summoned monsters and attacked them, wiping them out in an instant. Shay didn't take their souls as he had the other LID members that he'd attacked, as Declan had arrived by then. Masumi's memory was wiped off the Duel and rewritten to believe that Shay had been a member of LID.

Maiami Championship
At the Junior Youth Chamionship, Masumi's first match was against Zuzu in the afternoon. Zuzu asked Masumi why Shay was among them, and a confused Masumi replied that Shay had always been part of their group. Noticing that Zuzu was preoccupied before the Duel, Masumi commented that Zuzu's eyes held no luster. On her first turn, Masumi brought out "Gem-Knight Master Diamond" against Zuzu, who responded by revealing that she had learned to Fusion Summon, bringing out "Schuberta the Melodious Maestra" to not only destroy "Master Diamond," but also to prevent Masumi from recovering her "Gem-Knight Fusion" on the next turn. Masumi managed to climb back into the game by using "Brilliant Fusion" to call out her true ace monster, "Gem-Knight Lady Brilliant Diamond". In order to keep its ATK up, Masumi had to use Action Cards to pay the cost, consistently beating Zuzu to them. She reduced Zuzu to 100 LP, but Zuzu had read through Masumi's strategy of using Fusion Monsters to take control of Masumi's "Crystal Rose", which Zuzu used in the next turn to aid in Fusion Summoning "Bloom Diva the Melodious Choir". When her "Gem-Knight Zirconia" was destroyed, Masumi tried to use "Brilliant Spark" to finish Zuzu off, and discard an Action Card to prevent its activation, but Zuzu beat her to the card and finished Masumi off. "Bloom Diva" saved Masumi from a nasty fall, much to her embarrassment. Masumi later approached Zuzu outside the stadium and gave her "Crystal Rose", telling Zuzu that she wouldn't accept her losing in the tournament.

On the second day, she watched the Duels involving Gong, Yuya Sakaki and Silvio, and Shay. She commented to Yaiba that his disciple was doing terrible, though she was impressed when Gong won. During Silvio's Duel with Yuya, Masumi was impressed at Silvio's tactics, though she and her friends all expressed disdain at him. When Sora Shiun'in claimed that he was performing a real Fusion Summon, Masumi was offended, thinking that Sora was calling an LID Fusion Summon a fake. After Sora underestimated "Raidraptor - Rise Falcon", she and her friends commented that he'd be regretting doing so. She was impressed when Shay demonstrated his capability to Rank-Up his Xyz Monsters.

Masumi watched her friends' first round Duels; Dipper winning and moving onto the second round, but Yaiba being eliminated and physically beaten by Isao Kachidoki.

Different Dimensions
Masumi and a recovered Yaiba were present in the stands during the Battle Royal. When Henrietta revealed to the public the existence and MO of the Academy, she and Yaiba realized that this was the likely reason for Dipper's disappearance. Declan's announcement that LID would be training the Lancers prompted both Masumi and Yaiba to consider joining.

Deck
Masumi 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.