All appeals are dismissed.

The costs of appeal are assessed against the plaintiffs.

The grounds of appeal are examined.

1. As to the grounds of appeal against Defendant K, the Plaintiffs filed an appeal against Defendant K Co., Ltd. (hereinafter “Defendant K”) among the judgment below. However, the Plaintiffs did not state the grounds of appeal in the petition of appeal and the appellate brief did not state the grounds of appeal as to the grounds of appeal.

2. As to the ground of appeal against Defendant KB real estate trust company

A. As to the grounds of appeal Nos. 1 and 2, where a party to a contract directly provides a third party who has a different contractual relationship with the other party by shortening the process of performance through the instruction of the other party to the contract (the case of performance in the so-called triar relationship), and not only provides the benefits to the other party to the contract who has provided the benefits, but also provides the benefits to the third party, a party to the contract may not file a claim for return of unjust enrichment on the ground that the party received the benefits against the third party without any legal ground. In such a case, when a party to the contract can file a claim for return of unjust enrichment against the third party on the ground that the party to the contract received the benefits from the other party to the contract without any defects in legal relations as to the cause of the payment to the other party to the contract or the termination of the contract, transferring the risk burden under the contract under its own responsibility to the third party to the other party to the contract, thereby infringing on the other party’s right to defense against the other party to the contract (see, e.g., Supreme Court Decision 20036Da42714.