In the case you and your friend have purchased a real estate and renting out and receive rental fee, you and your friend need to file tax return respectively.
In real estate register, ratio of ownership is registered ( assumed you 70% : your friend 30% ).
If you and your friend earn 10 million yen in total, you can submit tax filing paper that your income is 7 million yen.
And your friend can declare amount of earning is 3 million yen, roughly speaking.
You and your friend can use basic deduction etc..