Nishikori, the world number eight, has carried on his form from the US Open - where he lost to Marin Cilic in the decider - with a deep run at the Malaysian Open in Kuala Lumpur.
The 24-year-old will carry the hopes of the home nation at the ATP 500 hard-court event, but he will be joined by at least three compatriots in the main draw - wildcards Go Soeda, Tatsuma Ito and Taro Daniel.
Nishikori - champion in Tokyo in 2012 - will fall outside the top four seeds, which will be occupied by Stan Wawrinka, David Ferrer, Milos Raonic and Jo-Wilfried Tsonga.
Swiss Wawrinka has not been in action on the ATP World Tour since losing in the New York quarter-finals to Nishikori.
Spaniard Ferrer, ranked fifth - one spot behind Wawrinka in fourth - was shocked at the Shenzhen Open in China on Thursday, losing to Viktor Troicki.
Champion here in 2007, Ferrer will want to bounce back with a strong performance in Japan.
Canada's Raonic has been a losing finalist the past two years in Japan, last year falling to Argentine Juan Martin del Potro - who is sidelined long-term with a wrist injury.
Tsonga, the 2009 champion from France, was a beaten quarter-finalist at one of his home tournaments in Metz in September, going down to David Goffin - but like Ferrer, he will be keen to atone in Asia.
Other top-20 players in the draw include Spain's Roberto Bautista-Agut and South Africa's Kevin Anderson.