Masumi Kōtsu

Masumi Kōtsu ( Kōtsu Masumi) is a character in the Yu-Gi-Oh! ARC-V anime. She is the Fusion Course Representative at Leo Duel School.

Appearance
Masumi appears to be taller than  Yaiba Tōdō, but still shorter than  Hokuto Shijima. She has red eyes and black hair that reaches past her shoulders. Masumi's outfit consists of a blue top and under that, she wears a one-pieced shirt and shorts which is a light yellow color. Underneath that, she wears black skin-tight shorts that end just above her knees. On her blue top, she wears her  LDS  pin. Her shoes are a dark blue. She puts her  Duel Disk  in a brown holster which she wears around her waist.

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 Yuzu 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 LDS 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 Shun 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.

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

You Show Duel School vs Leo Duel School
Masumi, Hokuto Shijima, and Yaiba Tōdō were enlisted by Himika Akaba to Duel members of the You Show Duel School in retaliation for the apparent attack on Shingo. After Hokuto was defeated by Yūya Sakaki, Masumi went next, matched up against Yuzu Hīragi. Before the Duel, Masumi noted that Yuzu's eyes had no shine to them, much to Yuzu's irritation. She brought out "Gem-Knight Paz" on her first turn, but took a large amount of damage from Yuzu's "Melodious" monsters. On her next turn, however, reiterating her comments on Yuzu's lack of brilliance, she brought out both "Gem-Knight Crysta" and "Gem-Knight Master Dia," using the effects of the latter to set up a One Turn Kill. Yuzu attempted to use an Action Card to stop the second attack of "Master Dia," 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 Yūya and Yuzu's embrace after the Duel, prompting Yuzu's swift breaking up of the situation. Yaiba went next, Dueling Gongenzaka and claiming to be far stronger than "those weaklings", which infuriated Hokuto. Masumi admitted that the comment was annoying, but Hokuto had lost, after all, prompting an embarrassed Hokuto to sulk in the corner. During Yaiba's Duel, Hokuto 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 Hokuto to retreat to the corner in shame. After Yaiba and Gongenzaka drew the Duel, Himika proposed a tie-breaker Duel between those who had won; Yūya and Masumi. Masumi was ready to Duel, but they were interrupted by Reiji Akaba.

LDS Investigation
Upon learning that her Fusion teacher, Marco, had been in an incident, Masumi becomes frantic about him. Unconvinced by Tio's reassurances that the LDS 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 Yuzu's bracelet, infuriating Masumi and causing her to accuse Yūya, who had just arrived, of being in cahoots. She dashed off after Sora tricked her into thinking he had run past, while pushing Yūya away.

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

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

Round 1
At the Junior Youth Championship, Masumi's first match was against Yuzu in the afternoon. Yuzu asked Masumi why Shun was among them, and a confused Masumi replied that Shun had always been part of their group. Noticing that Yuzu was preoccupied before the Duel, Masumi commented that Yuzu's eyes held no luster. On her first turn, Masumi brought out "Gem-Knight Master Dia" against Yuzu, who responded by revealing that she had learned to Fusion Summon, bringing out "Meisterin Schubert the Melodious Maestra" to not only destroy "Master Dia," 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 Dia". In order to keep its ATK up, Masumi had to use Action Cards to pay the cost, consistently beating Yuzu to them. She reduced Yuzu to 100 LP, but Yuzu had read through Masumi's strategy of using Fusion Monsters to take control of Masumi's "Crystal Rose", which Yuzu used in the next turn to aid in Fusion Summoning "Bloom Diva the Floral Melodious Saint". When her "Gem-Knight Zirconia" was destroyed, Masumi tried to use "Brilliant Spark" to finish Yuzu off, and discard an Action Card to prevent its activation, but Yuzu beat her to the card and finished Masumi off. "Bloom Diva" saved Masumi from a nasty fall, much to her embarrassment. Masumi later approached Yuzu outside the stadium and gave her "Crystal Rose", telling Yuzu that she wouldn't accept her losing in the tournament.

Round 2
On the second day, she watched the Duels involving Noboru Gongenzaka, Yūya Sakaki and Shingo Sawatari, and Shun Kurosaki. She commented to Yaiba that his disciple was doing terrible, though she was impressed when Gongenzaka won. During Shingo's Duel with Yūya, Masumi was impressed at Shingo'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 LDS Fusion Summon a fake. After Sora underestimated "Raid Raptors - Rise Falcon", she and her friends commented that he'd be regretting doing so. She was impressed when Shun demonstrated his capability to Rank-Up his Xyz Monsters.

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

Synchro Dimension Arc
Masumi and a recovered Yaiba were present in the stands during the Battle Royal. When Himika Akaba revealed to the public the existence and MO of Academia, she and Yaiba realized that this was the likely reason for Hokuto's disappearance. Reiji's announcement that LDS 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 Dia", which is later replaced by "Gem-Knight Lady Brilliant Dia". 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 Dia" by copying the effect of "Gem-Knight Paz" 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 Dia", 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.