This study demonstrates high-order nonlinear magnonics in an antiferromagnetic orthoferrite, Sm₀.₄Er₀.₆FeO₃, using resonant THz pulse pairs. The research shows that intense, resonant THz magnetic fields enable high-order magnon multiplication, distinct from conventional nonlinear effects like high harmonic generation. The team used THz multi-dimensional coherent spectroscopy (THz-MDCS) to detect nonlinear magnon interactions up to six magnon quanta in strongly-driven many-magnon correlated states. The results reveal 7th-order spin-wave mixing and 6th harmonic magnon generation, indicating significant nonlinear magnon interactions. The study highlights the role of four-fold magnetic anisotropy and Dzyaloshinskii-Moriya (DM) symmetry breaking in the observed nonlinear magnon effects. The results also suggest that quantum fluctuations are inherent in nonlinear magnons. The THz-MDCS technique allows for the detection of high-order nonlinear magnon processes, including up to sixth harmonic generation and various wave mixing processes. The simulations support the experimental findings, showing that the observed nonlinear magnon peaks arise from the interplay of DM interaction and four-fold magnetic anisotropy. The research demonstrates that THz-MDCS can achieve super-resolution tomography of magnon interactions and nonlinearity, revealing the underlying physics of high-order magnon multiplication. The results emphasize the importance of considering quantum spin fluctuations in describing THz-MDCS experiments. The study also shows that the THz-MDCS technique can resolve nonlinear interactions between coherent magnons excited by different pulses, allowing for the association of these interactions with specific peaks in 2D frequency space. The findings have implications for the development of nonlinear quantum magnonics, which could be pursued in parallel with nonlinear quantum optics. The study provides a deeper understanding of the quantum properties of spins and their role in nonlinear magnonics. The results suggest that the observed high-order magnon nonlinearities exceed predictions from classical spin models, highlighting the need for further investigation into the quantum nature of these interactions. The research also identifies the importance of considering factors such as THz electro-optic sampling response functions and THz propagation effects in future quantitative analyses of high-order magnon nonlinear peaks.This study demonstrates high-order nonlinear magnonics in an antiferromagnetic orthoferrite, Sm₀.₄Er₀.₆FeO₃, using resonant THz pulse pairs. The research shows that intense, resonant THz magnetic fields enable high-order magnon multiplication, distinct from conventional nonlinear effects like high harmonic generation. The team used THz multi-dimensional coherent spectroscopy (THz-MDCS) to detect nonlinear magnon interactions up to six magnon quanta in strongly-driven many-magnon correlated states. The results reveal 7th-order spin-wave mixing and 6th harmonic magnon generation, indicating significant nonlinear magnon interactions. The study highlights the role of four-fold magnetic anisotropy and Dzyaloshinskii-Moriya (DM) symmetry breaking in the observed nonlinear magnon effects. The results also suggest that quantum fluctuations are inherent in nonlinear magnons. The THz-MDCS technique allows for the detection of high-order nonlinear magnon processes, including up to sixth harmonic generation and various wave mixing processes. The simulations support the experimental findings, showing that the observed nonlinear magnon peaks arise from the interplay of DM interaction and four-fold magnetic anisotropy. The research demonstrates that THz-MDCS can achieve super-resolution tomography of magnon interactions and nonlinearity, revealing the underlying physics of high-order magnon multiplication. The results emphasize the importance of considering quantum spin fluctuations in describing THz-MDCS experiments. The study also shows that the THz-MDCS technique can resolve nonlinear interactions between coherent magnons excited by different pulses, allowing for the association of these interactions with specific peaks in 2D frequency space. The findings have implications for the development of nonlinear quantum magnonics, which could be pursued in parallel with nonlinear quantum optics. The study provides a deeper understanding of the quantum properties of spins and their role in nonlinear magnonics. The results suggest that the observed high-order magnon nonlinearities exceed predictions from classical spin models, highlighting the need for further investigation into the quantum nature of these interactions. The research also identifies the importance of considering factors such as THz electro-optic sampling response functions and THz propagation effects in future quantitative analyses of high-order magnon nonlinear peaks.