Sei Kato is an ICRR fellow at the Institute for Cosmic Ray Research at the University of Tokyo. His work is concerned with the calibration of the ALPAQUITA detectors which started the data acquisition in September 2022 and continues the analysis of the data obtained by the Tibet air shower array. He received his master of science and Ph.D. from the University of Tokyo in 2020 and 2023, respectively.Reconstructing the gamma-ray energy spectra of two gamma-ray sources, TASG J1844-038 and HESS J1849-000, up to the sub-PeV rfange in combination with the analysis of the published CO line emission data, he discussed in detail the origins of the observed gamma rays and suggested that these two gamma-ray sources are candidates for Galactic PeVatrons.He was honored with the School of Science Encouragement Award of the University of Tokyo in 2023 and the Student Presentation Award of the Physical Society of Japan in 2020, 2023.