Moriuchi was born on October 10, 1970, in Yokohama.[1] His grandfather was shogi professional Yukio Kyōsu [ja], who died about ten years before Moriuchi was born. When Moriuchi was young and would visit his grandmother's house, she would show him old issues of Shogi World that she had kept, and this is when Moriuchi first became interested in shogi.[2]
Moriuchi started playing in shogi tournaments as an elementary school student and it was there that his rivalry with Yoshiharu Habu began. Habu lived in neighboring Tokyo and was the same age, so the two often participated in the same tournaments.[3] Moriuchi even went to watch Habu win a tournament whose entry was limited to Tokyo residents only. The following year, Moriuchi defeated Habu in the finals of the same tournament after it had been changed to an open tournament allowing anyone to participate.[2]
In 1982, Moriuchi finished tied for third in the 7th Elementary Student Shogi Meijin Tournament [ja]. Both Moriuchi and Habu advanced to the semi-finals held in Tokyo which were broadcast on television. Moriuchi, however, lost his semi-final game, whereas Habu won his and then subsequently the final to become the "7th Elementary School Shōgi Meijin".[2] That same year, Moriuchi entered the Japan Shogi Association's apprentice school with the rank of 6-kyū as a protegee of shogi professional Osamu Katsūra [ja]. He was awarded professional status and the rank of 4-dan in May 1987.[2]
In 1987, Moriuchi won his first professional shogi tournament when he defeated Hiroyuki Iida [ja] 2 games to none to win the 18th Shinjin-Ō [ja], but was unable to repeat as champion the following year when he lost the 19th Shinjin-Ō to Habu 2 games to none in the first match between the two as professionals. Moriuchi would, however, win the tournament again in 1991 (against Taku Morishita, 2–0) and 1993 (against Yasumitsu Satō, 2–1).[2][4]
In 1988, Moriuchi defeated then MeijinKoji Tanigawa 2 games to 1 to win the 7th All Nihon Pro [ja]. The victory was a much discussed through the year in professional shogi circles because Moriuch ranked 4-dan at the time had defeated the reigning Meijin in a match.[2] Tanigawa would get his chance for revenge against Moriuchi in 19th All Nihon Pro Tournament final in 2000, but was defeated 3 games to 2.[5]
Moriuchi's first appearance in a major title match was the 54th Meijin Match in June 1996. Moriuchi was promoted to the Class A League for the first time in 1995 and went on to win the league in his first season with a 7–2 record to advance to the title match against Habu. Although both players were the same age and had been rivals since elementary school, Habu was much more establish as a professional and was also a 7-crown title holder (i.e., simultaneously held all seven major titles) at the time. Moriuchi ended up losing the matchi 4–1.[2][6]
Moriuchi became the fifteenth shogi professional to win 800 official games when he defeated Yoshiharu Habu in Game 2 of 69th Meijin title match on April 21, 2011.[7]
In March 2017, Moriuchi voluntarily declared himself as a free class player, thus leaving the Meijin tournament league.[8][9]
Moriuchi is considered an all-around player proficient at both Static Rook and Ranging Rook strategies. Although he's widely known as defensively strong player, his style often called "iron-clad" or "steel defense"; in the opinion of shogi professionals Hirotaka Nozuki and Akihito Hirose, however, his most characteristic trait is his ability to switch from defense to attack. His so-called "strong" style is often contrasted with the "gentle" one of Yoshiharu Habu.
Moriuchi is also well known for the Moriuchi Fortress variation which is characterized by pushing the pawn at the ninth file with P. 9d instead of the traditional P-8e, followed then by a knight jump to 9-c and then 8e.
Moriuchi has appeared in major title matches a total of 25 times. He has won the Meijin title eight times, thus qualifying for the Lifetime Meijin title. He has also won the Ryūō title twice, and the Kiō and the Ōshō titles once each.[11] In addition to major titles, Moriuchi has won thirteen other shogi championships during his career.[12]
Moriuchi has received a number of awards and honors throughout his career for his accomplishments both on an off the shogi board. These include awards given out annually by the JSA for performance in official games as well as other JSA awards for career accomplishments, and awards received from governmental organizations, etc. for contributions made to Japanese society.[13][14]
Note: All amounts are given in Japanese yen and include prize money and fees earned from official tournaments and games held from January 1 to December 31.
Moriuchi also plays chess and backgammon. He been playing in chess tournaments since 1998,[30] and his chess Elo score is 2310 (FIDE Master level) as of January 2018[update].[31]
In August 2014, he tied for fourth in the 39th Backgammon World Championship held in Monte Carlo.[32][33]