The person who is aiming to start a business in Japan is required to have Investor Manager Residential status(VISA). As follows there is requirements for issuing it.
http://www.moj.go.jp/nyuukokukanri/kouhou/nyuukokukanri07_00088.html
About the office. We often asked that is it possible to share the office or rent the office partially. It is possible but should be parted physically and prepare the contract documents properly. The contract with the sublessee and agreement with the landlord and the agreement of the utility charges.
We are happy to support your contract note preparation for the investor manager visa application so please contact us.
