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Wet-strength resins are fundamentally important for papers as they provide water resistance and wet strength, allowing papers to complete tasks before incurring wet damage. Resins currently in use are primarily petroleum-based substances that pose inherently environmental and health risks due to the release of hazardous organochlorine or formaldehyde compounds during production and use. While bio-based resins provide a more sustainable alternative, they typically present insufficient wet-strength performance. Yet, the ever-growing demand for paper products calls for more sustainable and greener resins. Herein, guanidinylated cluster-modified chitosan (3.44 mmol/g cationic charge content) has been obtained as an alternative wet-strength resin. The strategy is based on grouping cations into ion clusters which interact with cellulosic fibers, thereby enhancing the electrostatic force and facilitating a robust and multifaceted interactive physical network. As a result, the fabricated benign papers display ~57 MPa dry strength and ~ 3 MPa wet strength at 1 wt% dosage. The values are 3 and 10 times higher than control papers (17.3 and ~ 0.35 MPa, respectively), and are comparable to those of 1 wt%-PAE-reinforced papers. In addition, re-exposing papers to water enabled us to observe their good dispersibility and antibacterial behavior. Overall, this work presents an alternative biomass-derived wet-strength resin.