Golez: The US and Japan are ironclad allies under their Treaty of Mutual Cooperation and Security as amended in 1960. An attack on one is considered an attack on the other.
Japan has a very modern and powerful Navy which includes several Aegis destroyers (Atago and Kongo class) that can protect a carrier and other targets from missile attack.
"The Aegis Ballistic Missile Defense System (Aegis BMD or ABMD) is a United States Department of Defense Missile Defense Agency program developed to provide missile defense against short to intermediate-range ballistic missiles. It is part of the United States national missile defense strategy. Aegis BMD (also known as Sea-Based Midcourse) is designed to intercept ballistic missiles post-boost phase and prior to reentry.
"It enables warships to shoot down enemy ballistic missiles by expanding the Aegis Combat System with the addition of the AN/SPY-1 radar and Standard missile technologies. Aegis BMD-equipped vessels can transmit their target detection information to the Ground-Based Midcourse Defense system and, if needed, engage potential threats using either the SM-2 or SM-3 missile. Aegis BMD does not have the ability to intercept ICBMs, although future versions may allow limited intercept capability.
"The current system uses the Lockheed Martin Aegis Weapon System and the Raytheon RIM-161 Standard Missile 3 (SM-3). Notable subcontractors and technical experts include Boeing Defense, Space & Security, Alliant Techsystems (ATK), Honeywell, Engility, Naval Surface Warfare Center, SPAWAR Systems Center, Johns Hopkins University Applied Physics Laboratory (JHU/APL), and the Massachusetts Institute of Technology Lincoln Laboratory (Lincoln Lab)."