The Reversal of a Son-in-law - Chapter 16 Do Not Cross My Bottom Line

Akira Kisaragi traverses into the Bleach world, unlocking a check-in system.He initially thought that by checking in daily, he could become stronger, soon become the Captain-Commander, join Division Zero, punch Yhwach, kick the Soul King, and marry Unohana...However, the system's style wasn't quite what he had imagined.〈 Check-in complete, obtained Genryūsai Yamamoto's secret roasted sweet potato! 〉〈 Check-in complete, obtained exclusive attribute: King of Normal Attacks, effect... 〉〈 Check-in complete, obtained Retsu Unohana's... 〉Akira's eyes suddenly lit up!“Seems like this might not be so bad after all!”

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.

This crossing is so strange, death crossing, game crossing, etc. are probably barely acceptable, but why can you cross even if the fish tank is broken?

and actually passed through the magic tree in “OVERLORD” that is said to be able to destroy the world?

No! It is sad enough to regenerate into a plant. The protagonist, Ainz Ur Gong, the undead king, has also accepted the adventurer’s guild mission and wants to kill me!

I want to change my destiny! Live! I want to-surrender!

Ainz: Since he has accepted the job commission from the Adventurer’s Guild, deliberate failure is detrimental to the prestige of Ainz Ul Christine (the “surrender” button has been deducted)

actually died as soon as he crossed, but there is still a chance to return~ from the beginning of the magic tree to this world.

I must change my destiny this time! Live!

- Description from novelbuddy

The story begins with the last day of Yggdrasil, a popular online game which is being quietly shut down. Our protagonist Momonga decides to stay in his beloved game until the last moment, so waits for the forced logout. Unexpectedly, the server does not shut down and Momonga is stuck in a skeleton avatar in another world. “The powerful Overlord” needs now to discover the new world and face the continuous challenges that arise.