7th Demon Prince Jilbagias' Chronicle of Demon Kingdom Toppling - Chapter 86.1 - Spread Your Wings

Yukima Azuma—charismatic, confident, and utterly unforgettable. He was the man every girl wanted but could never truly keep. One by one, they fell for him, only to be left with memories they couldn’t erase.Kasumigaoka Utaha: “I was his first, the one who taught him love… only for him to use it on other women.”Sawamura Eriri: “If I hadn’t been such a tsundere, maybe things would have been different.”Yukinoshita Yukino: “He was my light in the darkness, the only one who ever truly saw me.”Yukinoshita Haruno: “That bastard ran away after taking everything from me.”Hoshino Ai: “My only true love. The one I can never replace.”And when asked about their relationship with him?“Ex-girlfriend.”But to the women still in his life?Sora Ginko, Kato Megumi, Sagiri, Bocchi, Shinomiya Kaguya, Kirisu Mafuyu, Suou Yuki, Alya—“Thieving cats.”Because no matter how much time passed, no matter how far he went—one truth remained: Yukima Azuma was the one man they could never forget.

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.

Reborn into a failing noble family, Liu Xingchang awakens in a weakened teenage body, surrounded by humiliation and betrayal. Once the revered Sword God of the Northern Polar Heaven Domain, he now faces ridicule from his former lover, Yu Qiuer, who has abandoned him for a rival, and scorn from the very man daring to tread on his legacy.Though his power has diminished to a mere third-grade cultivation, Liu’s indomitable spirit drives him to reclaim his path to supremacy. When he fatally strikes his foe amidst the disbelieving crowd, even the noble Princess Qingyuan is drawn to this fallen “”coward’s”” defiant strength.Can Liu Xingchang resurrect his family’s honor, ascend to the Divine Realm, and turn the tables on those who scorned him?

She is one of the best thieves that the world has seen in the 24th century. However, not even in her wildest dreams had she imagine that she’d be reincarnated as a good-for-nothing orphaned Seventh Miss of the Vermilion Bird Family. She finds herself stuck in a family that mistreats her, as well as an unfamiliar place with no support system.