Active M dwarfs exhibit frequent and energetic flares that provide a unique laboratory for studying chromospheric heating processes under extreme magnetic activity. To probe the flare process of M-dwarfs, we present a high-resolution (R ∼ 30,000) spectroscopic case study of a superflare onADLeo, detected on 2023 March 14 using the Bohyunsan Optical Echelle Spectrograph (BOES). Such high-energy events are rarely captured with simultaneous multi-line spectroscopy, allowing us to trace the energy partition and temporal evolution of the chromospheric lines. Based on equivalent width variations, we found that the Hα line radiated 8.8×1030 erg, implying a total bolometric energy (∼1033 erg) comparable to the largest solar flares. The Balmer series dominated the energy budget; the individual Ca ii H and K lines contributed 47.5% and 26.2% of the Hα energy, respectively, while each Ca ii infrared triplet line emitted ∼17–19%. We confirm that the delayed peak emission, previously reported for Ca ii H&K, also occurs in the Ca ii triplet and Na i lines. These delays are consistent with the Neupert effect, suggesting that cumulative heating governs the gradual phase emission. While this superflare resembled solar flares in its general morphology, it also displayed systematic differences in chromospheric emission. It is likely that these differences reflect the distinct atmospheric structure and quiescent chromospheric conditions of M dwarfs, rather than fundamentally different flare physics.

Introduction
Observations and Data Reduction
    Target Description and Observations
    Data Reduction
Data Analysis
    Line Flux Measurement and Energy Estimation
    Line Selection
Results
    Development of the Superflare
    Radiated Energy Budget
    Temporal Evolution of Line Profiles
Discussion
    Stratified Chromospheric Response: Evolution of Impulsive and Gradual Emissions
    Comparison with Previous AD Leo Flare Studies
    Comparison with a Solar Flare
Summary
Acknowledgments
References
Additional Line Profiles

• Younghun Oh(Department of Physics & Astronomy, Seoul National University, Seoul 08826, Republic of Korea)
• Jongchul Chae(Department of Physics & Astronomy, Seoul National University, Seoul 08826, Republic of Korea) Corresponding author
• Soosang Kang(Department of Physics & Astronomy, Seoul National University, Seoul 08826, Republic of Korea)
• Kyeore Lee(Department of Physics & Astronomy, Seoul National University, Seoul 08826, Republic of Korea)
• Seo-Won Chang(Department of Physics & Astronomy, Seoul National University, Seoul 08826, Republic of Korea, SNU Astronomy Research Center, Astronomy Program, Department of Physics and Astronomy, Seoul National University, Seoul 08826, Republic of Korea) Corresponding author
• Kyoung-Sun Lee(Department of Physics & Astronomy, Seoul National University, Seoul 08826, Republic of Korea, SNU Astronomy Research Center, Astronomy Program, Department of Physics and Astronomy, Seoul National University, Seoul 08826, Republic of Korea)
• Juhyung Kang(Korea Astronomy and Space Science Institute, Daejeon 34055, Republic of Korea)
• Hyun-Il Sung(Korea Astronomy and Space Science Institute, Daejeon 34055, Republic of Korea)
• Eun-Kyung Lim(Korea Astronomy and Space Science Institute, Daejeon 34055, Republic of Korea, Astronomy and Space Science, University of Science and Technology, Daejeon 34113, Republic of Korea)