[1] His grandfather was shogi professional Yukio Kyōsu [ja], who died about ten years before Moriuchi was born.

[2] Moriuchi started playing in shogi tournaments as an elementary school student and it was there that his rivalry with Yoshiharu Habu began.

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] 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.

[2][4] In 1988, Moriuchi defeated then Meijin Koji 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.

[7] In March 2017, Moriuchi voluntarily declared himself as a free class player, thus leaving the Meijin tournament league.

Moriuchi has received a number of awards and honors throughout his career for his accomplishments both on an off the shogi board.