An axion, or axion-like particle, is a pseudoscalar particle with well-controlled properties dictated by shift symmetry. Notably, an axion can play a crucial role in refining the description of the Standard Model (SM) in various aspects: (i) serving as a compelling candidate for the unknown degrees of freedom like dark matter and inflaton, (ii) enhancing the naturalness of the SM by resolving issues such as the strong CP problem and the gauge hierarchy problem, and (iii) providing a plausible explanation for the matter-antimatter asymmetry in the universe. Intriguingly, axions can be investigated through astrophysical and cosmological observations as well as laboratory experiments. In this talk, I will provide a brief review of axion physics and introduce my recent works on how axionic extensions address the challenges faced by the SM. Also, I wish to invite engaging discussions on axions for those interested.