From Ex-Im Bank of U.S. v. Advanced Polymer Sciences, Inc., 2009 U.S. Dist. LEXIS 18855 (N.D. Ohio Mar. 11, 2009) (applying Ohio law):

"Res judicata extinguishes 'all rights of the plaintiff to remedies against the defendant with respect to all or any part or [sic] the transaction, or series of connected transactions, out of which the action arose.'" Walker v. Gen. Tel. Co., 25 Fed. Appx. 332, 336, 2001 WL 1667282, at *3 (6th Cir. 2001) (citing J.Z. G. Res., Inc. v. Shelby Ins. Co. , 84 F.3d 211, 215 (6th Cir.1996)). Thus, a second action is precluded when:

(1) there is a final decision on the merits of the first action by a court of competent jurisdiction; (2) the second action involves the same parties, or their privies, as the first; (3) the second action raises an issue actually litigated or which should have been litigated in the first action; and (4) there is identity of claims.

Walker, 25 Fed. Appx. at 336; accord Browning v. Levy, 283 F.3d 761, 771 (6th Cir. 2002).

One of the central concepts to res judicata is that when final judgment is rendered in favor of the plaintiff, the plaintiff can no longer maintain an action on the original claim. The original claim, for instance a claim arising under a promissory note, is extinguished, and the plaintiff is left to pursue his rights under the judgment. Pub. Fin. Corp. of Warren v. Tate, 197 N.E.2d 825, 827 (Ohio Ct. App. 7th Dist. 1963). This concept is often referred to as merger, which, along with the concept of bar, forms the backbone of the doctrine of res judicata (also referred to as claim preclusion).

[Footnote 1.] As is often the case with legal nomenclature, a multiplicity of terms for the same doctrine has generated significant confusion in the law relating to the effect of former adjudication. Because both parties' briefs evidence confusion on this point, it bears emphasizing that res judicata broadly encompasses both claim preclusion and issue preclusion. But used more narrowly, the terms res judicata, claim preclusion, and estoppel by judgment are all different names for the same doctrine (which is composed of the complimentary concepts of merger and bar), as distinguished from collateral estoppel (also referred to as issue preclusion) which is a related but separate doctrine. In this opinion, res judicata refers exclusively to the doctrine of claim preclusion.

***"[R]es judicata is an affirmative defense which is waivable." *** This is because one of the primary purposes of the merger concept and res judicata in general is to prevent claim-splitting, in other words, "to protect the defendant from being harassed by repetitive actions based on the same claim." ***

In Davis [v. Sun Oil Co. , 148 F.3d 606, 611 (6th Cir. 1998)], the Sixth Circuit held that, under Ohio law, all existing claims arising out of a transaction merge into a judgment, "except where 'the parties have agreed in terms or in effect that the plaintiff may split his claim, or the defendant has acquiesced therein.'" 148 F.3d at 612 (construing Grava v. Parkman Township, 73 Ohio St.3d 379, 382-83 (Ohio 1995), as holding that Ohio adopts the RESTATEMENT (SECOND) § 26 approach to res judicata, which allows agreed claim-splitting). However, Davis involved acquiescence in the form of the defendant's failure to object when the plaintiff maintained two separate actions arising from the same transaction. See generally, 148 F.3d 606; accord Shaw v. Chell, 176 Ohio St. 375, 383 (Ohio 1964) (allowing claim-splitting where defendant failed to timely object). In contrast, the issue here is whether, by the cognovit provisions in the Guarantees [confessions of judgment] they signed, the Keehans explicitly, or in effect, agreed to allow claim-splitting. As no authority in the Sixth Circuit nor the state of Ohio definitively addresses the contention that parties may agree by contract to allow claim-splitting, this appears to be an issue of first impression.

Discussing the exception to the rule against claim-splitting when the parties have explicitly, or in effect, agreed to allow it, the Federal Court of Claims stated that "the parties may enter into an agreement, not directed to a particular contemplated action, which may have the effect of preserving a claim that might otherwise be superseded by a judgment." PCL Const. Servs., Inc. v. United States, 84 Fed. Cl. 408, 429 (Fed. Cl. 2008) (discussing authority in favor of agreed claim-splitting); accord Herrmann v. Cencom Cable Assocs., Inc. , 999 F.2d 223, 225 (7th Cir. 1993) (parties may "agree to split a single claim into two or more suits"); Keith v. Aldridge, 900 F.2d 736, 740 (4th Cir. 1990) (consent by agreement "prevents the defendant from invoking claim preclusion"); Shelar v. Shelar, 910 F. Supp. 1307, 1313 n.4 (N.D. Ohio 1995) (stating in dicta that "courts normally acquiesce when the parties expressly agree to split a single cause of action"). Thus, the weight of authority appears to favor honoring the parties' agreement to allow claim-splitting.

Likewise, there is persuasive authority holding that when a transaction is structured so that the contract is divisible, this implicitly indicates that the parties have agreed to allow claim-splitting. In particular, when a contract for the payment of money is represented by a series of promissory notes, separate actions may be maintained on the different notes. Broyles v. Achor, 78 S.W.2d 459, 463 (Mo. Ct. App. 1935); Iowa Title & Loan Co. v. Clark, 247 N.W. 211, 214 (Iowa 1933); Ginsburg v. McBride, 226 N.W. 873, 874-75 (Mich. 1929); Gaddis v. Williams, 198 P. 483, 484 (Okla. 1921). The severability of the obligations represented by the various notes remains intact, even when all the notes are executed pursuant to a single transaction and all go into default simultaneously. Morrow v. Fitzpatrick, 131 S.E. 189 (Ga. Ct. App. 1926). Of particular relevance to the case at bar is Westinghouse Credit Corp. v. Kownslar, 496 S.W.2d 531 (Tex. 1973). There, the defendant had guaranteed payment of a series of promissory notes and the noteholder had already received judgment on some of the notes that were in default…. Each note represented a separate cause of action, and although the defendant had only signed a single guarantee, the defendant stood in the same relation to the debt as the original maker of the notes, against whom separate actions for each note could be maintained….

Because the Sixth Circuit has construed the Ohio Supreme Court's opinion in Grava as adopting the RESTATEMENT (SECOND) approach to claim-splitting, including allowing claim-splitting when a party acquiesces by failing to object, this Court is convinced that if presented with the issue, Ohio courts would follow the clear weight of authority with regard to explicit or implicit contractual agreement as well.