Chainer is an open-source deep learning framework designed for flexibility and intuitiveness, enabling researchers and developers to implement complex neural network models with ease. Originally developed by Preferred Networks, Chainer supports dynamic computation graphs that allow modifications to the network structure on-the-fly, making it suitable for cutting-edge research that requires iterative and evolutionary neural network modeling. Its straightforward and pure Python-based approach ensures that even novices in deep learning can grasp and implement their experiments swiftly.