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We present the discovery of the Type II supernova SN 2023ixf in M101 andfollow-up photometric and spectroscopic observations, respectively, in thefirst month and week of its evolution. Our discovery was made within a day ofestimated first light, and the following light curve is characterized by arapid rise ($\approx5$ days) to a luminous peak ($M_V\approx-18.2$ mag) andplateau ($M_V\approx-17.6$ mag) extending to $30$ days with a fast decline rateof $\approx0.03$ mag day$^{-1}$. During the rising phase, $U-V$ color showsblueward evolution, followed by redward evolution in the plateau phase.Prominent flash features of hydrogen, helium, carbon, and nitrogen dominate thespectra up to $\approx5$ days after first light, with a transition to a higherionization state in the first $\approx2$ days. Both the $U-V$ color and flashionization states suggest a rise in the temperature, indicative of a delayedshock breakout inside dense circumstellar material (CSM). From the timescalesof CSM interaction, we estimate its compact radial extent of$\sim(3-7)\times10^{14}$ cm. We then construct numerical light-curve modelsbased on both continuous and eruptive mass-loss scenarios shortly beforeexplosion. For the continuous mass-loss scenario, we infer a range of mass-losshistory with $0.1-1.0\,M_\odot\,{\rm yr}^{-1}$ in the final $2-1$ yr beforeexplosion, with a potentially decreasing mass loss of $0.01-0.1\,M_\odot\,{\rmyr}^{-1}$ in $\sim0.7-0.4$ yr toward the explosion. For the eruptive mass-lossscenario, we favor eruptions releasing $0.3-1\,M_\odot$ of the envelope atabout a year before explosion, which result in CSM with mass and extent similarto the continuous scenario. We discuss the implications of the availablemultiwavelength constraints obtained thus far on the progenitor candidate andSN 2023ixf to our variable CSM models.

From Discovery to the First Month of the Type II Supernova 2023ixf: High and Variable Mass Loss in the Final Year before Explosion