Blackstone has emerged as the frontrunner to buy a mixed-use office complex in Tokyo being sold by Seibu Holdings in a deal that could be worth around ¥400 billion ($2.6 billion), according to people familiar with the matter.

Seibu has chosen to work with the U.S. alternative investment firm for the sale of its Tokyo Garden Terrace Kioicho after a months-long bidding process, said the people, who asked not to be identified because the matter is private.