Thunder Force III went on sale for the Mega Drive in June 1990. It was a shoot-'em-up from Technosoft, a company that had already made its name on fast, loud, tightly built games. Music for the game was credited to a small group of composers. One of the names was Toshiharu Yamanishi, who is listed as having begun his career on this very game.
That is nearly everything the record can say about the beginning. Yamanishi was born in 1971, according to the Japanese Wikipedia, which cites no source for it. There is no interview from this period that I could find, no account of how he came to Technosoft, and no sentence in which he describes what it was like to write for the game. What exists is the credit itself, and the credit is enough to start from: Thunder Force III, with Tomomi Ohtani. The sound driver on that console had been written by Naosuke Arai, a colleague at the same company.
In December 1990 he was credited with sound effects on Elemental Master. In July 1992 he returned to the series for Thunder Force IV, this time alongside Takeshi Yoshida. The Mega Drive's sound chip gave composers a few channels and a very hard ceiling. The game's tempo, its drums and its melody all had to fit inside it. These two Thunder Force soundtracks are still the ones people name when they talk about what that console could do.
In 1995 he left Technosoft and joined Gust, a smaller company. His first Gust game was Falcata, released for the PlayStation in June 1995. A move from a studio built around arcade-style shooters to one making role-playing games is a large change of room. Why he made it is not recorded anywhere I could find, and I will not guess at it.
On May 23, 1997, Gust released Atelier Marie: The Alchemist of Salburg. It was a game with no final boss and no explosions. A young alchemist student tries to graduate by making things, one item at a time, and she has a limited number of days to do it. Yamanishi is credited here twice: as the game's director, and as a composer, sharing the soundtrack with Daisuke Achiwa. Reviewers of the soundtrack describe him as the main composer on the album. A 1998 sequel, Atelier Elie, credited the same two composers.
A track that sounds right in a battle can sound wrong in a room where someone is waiting for a mixture to finish. The same composer wrote for both rooms. One kind of music was made for a player's thumbs. The other was made for a player's patience.
After Gust, the picture grows faint. He worked for several other companies and under the alias Funky Surounin, a name he used for his own music. According to the Japanese Wikipedia, which is uncited on this point, a publisher's announcement in 2009 said that the music for one of its games had moved from his own company to another, and that his personal website became unreachable around the same time. In 2013 it was announced that he had joined a company called Exelion. There is no retirement notice and no stated reason for any of this, and no interview in which he explains.
What remains is the music, and it has outlasted every page that tried to explain him. People still play Thunder Force III and IV. Atelier Marie was remade in 2023, with its music rearranged by Kumi Tanioka, and the original soundtrack is still heard. You have a song you have carried for years, and the person who wrote it left no explanation of what they meant by it. If they never appear again, is the song still theirs, or has it become yours?