Even if a lease contract has been concluded and possession of the house and resident registration have been made, there are cases where opposability cannot yet be regarded as having arisen. These are cases where a lease relationship arises while possession of the house and resident registration continue to be maintained, so that the status of the possessor changes; in such cases, when opposability should be regarded as arising depends on when the existing resident registration is regarded as acquiring effect as a method of public notice that can satisfy the requirements for opposability.

Where the owner becomes a tenant: if the owner of a house, while living there with resident registration, disposes of the house to another person and then leases it back from the buyer and continues to live there, when should the opposability of that lease be said to arise? The reason the time at which opposability arises is a particular issue in such a case is that, for opposability to arise, it is not enough simply to have resident registration; the resident registration must have the effect of publicly notifying the existence of the lease so that third parties can clearly recognize it.

Where a person has resident registration at a certain place and that person is the owner of the real estate, a third party would ordinarily regard that resident registration as representing possession as an owner rather than possession as a tenant. Therefore, even if the owner has internally disposed of the real estate to another and is leasing it back and using it, as long as the registration of transfer of ownership has not been completed, that resident registration has no effect of publicly notifying the lease, and it must be said that only once ownership of the real estate is transferred to a third party does it acquire effect as a valid method of public notice satisfying the requirements for opposability.

In such a case, the court held: "Even though the lessor Eul acquired ownership of the apartment after concluding the lease contract with Gap and after Gap filed the move-in report, since the resident registration showed that Gap, who was not the owner, had been living there from the date of the move-in report, third parties could recognize that Gap's resident registration represented possession mediated by a lease rather than ownership; therefore, the resident registration had been performing the function of publicly notifying the lease from the date Gap completed the move-in report, and accordingly Gap acquired opposability of the lease immediately upon completion of the registration of transfer of ownership in Eul's name."

3. When opposability arises for a lease under a lease contract concluded between a former tenant without opposability and the successful bidder

Another case where a lease relationship arises and the status of the possessor changes is where, in auction proceedings, the successful bidder concludes a new lease contract, before paying the sale price, with a former tenant who has resident registration but no opposability.

For reference, case law holds that opposability arises from 0:00 a.m. on the day after delivery and resident registration are completed, and to get the deposit back with priority, a fixed date must be obtained together with opposability. Regarding when a former tenant who entered into a new lease with the successful bidder acquires opposability, there is a Supreme Court precedent holding that opposability is acquired immediately upon payment of the sale price, so check the original text together with the comparison of theories in the material. It is also useful to note that, under the 2023 amendment, a tenant can request information on senior fixed dates and unpaid taxes at the time of contracting.