Ishii was unable to secure a visa to leave Japan due to the recent earthquake and tsunami disasters that left the country's infrastructure in shambles and many without homes, food or electricity.
Larkin is unbeaten thus far in his MMA career, going 8-0 on the independent circuit. He owns a career victory over Strikeforce veteran Scott Carson. Lighty is a kickboxer who trains with UFC Hall of Famer Chuck Liddell.
Strikeforce Challengers 15 takes place at the Stockton Arena on Friday night and airs on Showtime at 11 p.m. ET/PT. It is the first Strikeforce card under the new Zuffa ownership.