TOKYO, Oct 28 (Reuters) - Japanese property developer Hulic Co will buy Tokyo-based Simplex Investment Advisors for about 155 billion yen ($1.29 billion), a person involved in the deal said on Wednesday.

Hulic is planning to sell all of Simplex's assets besides real estate properties to Mizuho Trust & Banking, a unit of Japanese mega-bank Mizuho Financial Group Inc, by December, the person said, asking not to be identified because the deal is not yet public.

U.S. investment fund Aetos Capital Real Estate had been looking for a buyer for Simplex, whose assets include hotels, office buildings, real estate trusts, and an asset management company.

($1 = 120.4700 yen) (Reporting by Junko Fujita; Editing by Chang-Ran Kim)