and I mean terrible in the heartbreaking way

From the End of the World - Girl gets her heart broken, so she goes into the past to try again. But she goes too far back and screws up the relationship she already had by erasing her past self.

And then she broke space-time and ended up in an apocalyptic world where everything she knows and loves is gone.

(THE SONG IS MUCH BETTER THAN I MAKE IT SOUND I SWEAR)

[Flaming June] Maeda Jun x Yanagi Nagi [Owari no Sek...

Wizard of the Volcano - Girl gets roped into going on an adventure with her friend. She finds a magic treasure, but the boy gets eaten by a dragon. She manages to save him, but now he's trapped in the volcano

[Flaming June] Maeda Jun x Yanagi Nagi [Hifukiyama n...

Executioner's Love - A guy is supposed to execute a girl, but she looks like an old lover, so he ends up saving her instead. He gets executed instead.

[Flaming June] Maeda Jun x yanagi nagi [Executioner ...

Invincible Soldier - A girl living in the slums gets beat up with the other thieves in the area. A soldier comes in and saves her, and so she follows him, hoping to learn his sword techniques.

But old thieving habits die hard, and her new father figure catches her in the act. They duel, and she wins, at the cost of his life.

[Flaming June] Maeda Jun x Yanagi Nagi [Muteki no So...

^my favorite if you can only watch one, make it this one