It's a Grade 3 like no other! And I should know, 'cause I'm an expert on the matter! Be wary! When I join forces with the strongest card ever created, it signals your doom! Dragonic Overlord the End! Super Strong Break Ride!
—Katsumi Morikawa, Episode 112
Katsumi Morikawa is a minor character in Cardfight!! Vanguard anime and manga. Despite katsu meaning "victory", he is one of the weakest deck builders in the anime (mostly due to the fact that his decks consist of too many grade 3s), but with a well-balanced deck he is actually a talented player.
He is very boastful and proud of his "strength," even though he has lost almost every Vanguard fight he has had, giving him the nickname "lose-umi" (often just called "loser" in the dub). He is very superstitious and regularly consults an astrology book. He also has a huge obsession with Team Ultra-Rare member Kourin and is often "fanboying" over her when he knows she's set to appear somewhere. For example, in episode 26, he implies he might have come to the nationals just to see Kourin instead of the actual fighting.
Morikawa is the self-professed strongest fighter in Card Capital. He starts the series off by stealing Aichi's Blaster Blade and betting it in a fight with Kai, attempting to use the rare card to beat him. While Morikawa is initially just a bully, he eventually lightens up and becomes Aichi's friend.
His favorite card is Juggernaut Maximum, but his deck has no set clan, as Morikawa attempts to stuff as many grade 3 cards into it as possible. Naturally, this causes him massive problems in successfully riding from one grade to the next, using his cards' skills, and activating triggers. Whenever he loses, he blames it on bad luck rather than poor deck-building choices. However, it's been shown in 51 and 52 that he actually is a good fighter, but only when using a deck that is good by itself.
Morikawa and Izaki graduated from Hitsue Junior High School and became students at Kai and Miwa's school, Hitsue High. Morikawa became very jealous of Aichi when Kourin moved into Aichi's class. Morikawa then decided to go to Miyaji Academy, but Aichi said that you weren't allowed to unless you were a student or a parent. Then Morikawa tried to declare himself the "father" of Aichi Sendou, but Kamui stopped him.
Vanguard G Season 2
In GIRS Crisis Morikawa hasn't changed at all, still being obsessed with Grade 3s, although now he does play single clan, Spike Brothers. He fought against Chrono, surprisingly being able to push Chrono into a corner by using his Grade 3s to attack efficiently, however he ended up losing anyways because every single card in his hand was Grade 3; thus he was unable to guard.
After the fight Chrono questioned why Morikawa is obsessed with Grade 3s. Morikawa said that he simply liked them, an answer that Chrono applauded.
Initially Morikawa steals Aichi's Blaster Blade as in the anime. As it happens, he's a member of Hitsue Junior High's CF Vanguard Research Club, sponsored by Mr. Mark. Unlike in the anime, Morikawa does not run a grade 3-centered deck, but instead uses a more traditional (and useful) Spike Brothers one (although during his first appearance, he does use Savage King which is a Tachikaze unit).
Morikawa's main deck is a Kagerō deck, with a random assortment of Grade 3s. It has more Grade 3s than any other grade, leaving him constantly with hands full of Grade 3s and nothing else to Ride.
It is shown he is actually an incredibly strong fighter when using a balanced deck, as shown in Ride 51 when he went to a shop tournament but forgot his deck. He was given a Golden Mechanical Soldier deck, and won every fight he had in the episode.
In Episode 112, Kai lends his Kagero deck to Morikawa, hoping to see how his strength compares to Aichi's through Morikawa, based on his old deck centered around his ace, Dragonic Overlord the End. This deck now uses the Break Ride unit Dauntless Drive Dragon as an alternative vanguard to ride the End on, granting it high power as well as the ability to re-stand if its attack fails to hit. This forces the opponent into a no-win situation; if they guard, it re-stands through Dauntless's skill, and if they don't, the End re-stands by its own skill instead, basically ensuring two attacks at least on that turn.
In Vanguard G Morikawa continues to play a mostly Grade 3 deck, though now he plays a full Spike Brothers deck likely due to Clan Fight regulations. His G-Unit Divine Hand, Good End Dragger allows him to actually put his excessive amount of Grade 3s to good use, but his deck's nature renders him unable to guard any attacks as usual.
(JP/EN dub): Gold glitters for eternity. And my glory glitters for eternity too! Tinkling, twinkling Gold Rutile!
(EN): Just in time to take the stage! I ride Juggernaut Maximum!
(EN): Dauntless Drive Dragon comes to save the day! Ride!
(EN): It's a Grade 3 like no other! And I should know because I'm an expert on the manner! Behold! When I join force with the strongest card ever created, it signals your doom! Dragonic Overlord, The End! Super Strong Breakride!
(EN): Here goes! Twinkle, Twinkle, Gold Rutile! I'm gonna win by a mile, Yeah!
(JP): His strength is neverending! My genius is also neverending! If two neverendings join hands, everything else comes to an end! I strongest break ride Dragonic Overlord the End!
(JP) Everyone, kneel before me! Then i'll become the scout' star!
The first character to ever appear on screen in the anime wasn't Aichi, Kai, or any other major character. It was Morikawa possessing Juggernaut Maximum.
It has been shown that Morikawa is actually a strong cardfighter when using a balanced deck; this is shown in Episode 51 and 52 where he used a trial deck given to him by Shin and achieved many victories, even against Aichi. Kai noted this as well and in episode 112 lent Morikawa his Kagero deck for his battle against Aichi. Morikawa gave Aichi a hard time, and even come close to defeating him, but in the end Aichi won.