Riichi Nishimoto is a Japanese voice actor born on April 20, 1976, in Sapporo, Hokkaido. He is affiliated with the talent management firm 81 Produce and made his debut as a voice actor in 2002. His first credited role was in the television anime Rockman EXE, where he voiced the character Kamen Rider.

Nishimoto's career includes a range of supporting and guest roles in numerous anime series throughout the 2000s. He is perhaps best known for his work in 2006, a year in which he appeared in several prominent and enduring titles. During this time, he voiced Ukyo in the comedy series Amaenaide yo!! Katsu!!, the role you mentioned. He also took on the part of Riki in the science fiction action series Innocent Venus, as you recalled. In addition to these, his 2006 roles included parts in acclaimed series such as Higurashi no Naku Koro ni (When They Cry) as various male villagers and town officials, The Melancholy of Haruhi Suzumiya as a baseball batter, and the fantasy series Ah My Buddha.

Throughout his career, Nishimoto has taken on a variety of character types, often playing unnamed supporting characters like police officers, soldiers, students, and townspeople. In 2005, he voiced the elderly man and righteous monk Ukyo in the first season of Amaenaide yo!!, a role he reprised for its sequel, Amaenaide yo!! Katsu!!, the following year. Other notable appearances from around this period include roles in Koi Kaze, Gintama, and the fantasy series The Familiar of Zero.

Beyond his television work, Nishimoto has contributed to theatrical anime films. He provided the voice of Kujira (the giant whale Pokémon) in the 2006 film Pokémon Ranger and the Temple of the Sea. He also voiced the character Spike in the critically acclaimed 2007 anime series Baccano! and performed the role of Beep in the science fiction series Zentrix, which you mentioned.

Nishimoto has also lent his voice to video games, such as the Croquette! series as Nigari, and to the Japanese dub of foreign media, including the children's series Bob the Builder. He has additionally participated in live-action television dramas and commercial voice-overs, including narration for a McDonald's commercial. His active period in the industry appears to have been primarily focused in the 2000s.