Sweet Love 1V1: Spoiled by The Executive - Chapter 2066

In the year 298 from the era of the gods, elementary school girls Sumi Washio, Sonoko Nogi, and Gin Minowa are tasked with an important mission. They are to become heroes and fight Vertex, a mysterious enemy that is attacking Shinju-sama, the god tree that protects Shikoku, the only area in the world that is still habitable. What they don’t know, is that this fight will cost them more than they could have ever imagined.

At Elysia's first meeting with the crown prince, her future fiance ended up punching him. In this way, she violated her first law of survival.

Elysia's three rules of survival - First, Stay away from the main couple of Adam and Eve and make sure they end up together. Second, never fall in love with anyone and keep yourself safe. Third, no matter what happens, make sure you are never caught in any act. Only then will Elysia be able to survive past her death on her 18th birthday.

Ever since her birth, Elysia Raffle knew a few secrets of this world. First, the world she had been born in was a book and Elysia was the villainess in that book. She was destined to be slain by Adam on her 18th birthday and the day of their marriage.

Elysia needed to keep a distance from the main couple to avoid that fate. But how did she do it when she was engaged with one of the main parties and the other refused to leave her alone?

Now Elysia needed to do everything possible in her power to ensure that her engagement with the crown prince was broken and the main couple ends up together.

But it was easier said than done.

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.