Oxygen storage amount estimation device, oxygen storage amount estimation system, controller for internal combustion engine, data analysis device, and method for estimating oxygen storage amount

An oxygen storage amount estimation device estimates an oxygen storage amount of a catalyst disposed in an exhaust passage of an internal combustion engine. The oxygen storage amount estimation device includes a storage device and processing circuitry. The storage device stores mapping data, which is data specifying a mapping that uses multiple variables including at least an excess-deficient amount variable and a previous value of a storage amount variable as an input to output a value of the storage amount variable. The processing circuitry executes a storage amount variable calculation process that repeatedly calculates a value of the storage amount variable based on an output of the mapping using the multiple variables and an operation process that operates predetermined hardware based on a calculation result of the storage amount variable calculation process. The mapping data includes data learned by machine learning.