These Epsilon specs are very similar to the developed but cancelled US MX ICBM. MXs specs are Height 22m, Diameter 2.3m, Weight 97 tons, 3 stages, blast yield 3 Mt total (using up to 10 MIRVs).
Modern ballistic missiles generally have solid fuel stages (for quicker preparation and more rugged handling) rather than liquid fuel typically used in civilian rockets. So it is notable that the first, second and third stages of the Epsilon are solid fuel.
The extent to which the US assisted JAXA's Epsilon Project is unclear. Japan Aerospace eXploration Agency (JAXA) is Japan’s NASA equivalent. Space agencies have dual military-civilian use technology and dual-use career personnel.