Raising A Few Wives in a Beast Apocalypse - Chapter 217: Clarity from Iris...

Protagonist travels between different anime worlds to right wrongs and uncover his reason for being along the way.

- Description from Novelupdates

Side story of Kyoukai Senjou no Horizon bundled with the first press release of the 1st, 3rd, 5th and 7th Blu-ray volumes of both seasons of anime.

This side story follows Asama, Kimi and Mitotsudaira aboard Musashi one year before the beginning of the main story, as Asama is considering to create a music band together with her two friends for the next festival in Aki, a territory under the governance of K.P.A. Italia.

Tao Xiaodong had a blind brother. Tang Suoyan, gentle and calm, was his brother’s favourite doctor. As such, Tao Xiaodong loved Tang Suoyan as well.

Oftentimes, people lose sight of that which was easily gained.

Over the years, Tong Ning was so coddled by Tang Suoyan that he failed to appreciate how fetching this rare specimen was—dumping him without pause, and picking him up again when he had a change of heart.

Except, this time, he was a step too late. Tao Xiaodong had long made his move.

Tao Xiaodong looked at Tong Ning, telling him with a smile, “It doesn’t matter who Tang Suoyan used to be with. He’s mine now. As long as I don’t let go, you’ll never be able to take away what I hold onto.”

- Description from Novelupdates

A scientific genius named Thomas Harrier was transmigrated to an imperial prince body after a car accident that took his life. He found out that he is in a world similar to our own with a timeline akin to early twentieth century. The body that he is occupying was the imperial prince of a failing empire who suddenly rose to power after a successful assassination attempt of his father. Unaware that the attack is just the beginning of what is to come. He faces many challenges throughout. Will Thomas Harrier be able to live his second life in peace while running an empire and getting it back to its former glory? Or will he succumb into a conspiracy lurking within the country's borders?

Expect some:

Cold war era techs.

Super battleship with advanced electronics, propulsion, and fire control systems?
Helicopters?
Missiles?
Modern medicines and equipment?
AC-130?
A nuke?
Challenger or Abrams or Leopard?
F-4 Phantom or MIG-21?
Colored TV's.

Everything!!!

PS. Cover not mine, I just found it on google.