Boonie Bears: I'm Longya, and I'm Invincible

Long Xuan is an ordinary middle school student. On the day he finishes his college entrance exams, he goes to pick up the Kamen Rider Ryuga Advent Deck and belt he bought online. A hundred-ton truck sends him to the world of Kamen Rider Ryuki, where he becomes Kamen Rider Ryuga.

In the Mirror World Rider War, he goes on a winning streak, defeats every Rider, and obtains the Survive Card. With it, he unlocks Survive Ryuga and defeats Odin.

After beating Odin, fate seems to play a joke on him: he transmigrates again, this time to the world of Boonie Bears. Once there, Long Xuan discovers that something is off about this world. A Rider War is taking place here too, and even some tokusatsu villains have shown up.

Still, the villains don't get in the way of his life in Gou Xiong Ling. He takes it easy when he can and lies flat when he wants, until the System appears and forces him onto the path of upholding justice and peace.

Long Xuan: I finally fought my way through the Rider War, and now I can't even rest? Are you screwing with me? Damn it.

(One heroine + with or without a System + decisive and ruthless + invincible. Note: The System is pretty useless. It only occasionally sends the protagonist gear, whenever it feels like it.)