Natsu stiffens the moment he hears the sound. The sound of someone's heart beating, heavy breaths and pained groans. He recognises the source, of course he does, every single thing about her is ingrained in his system. There's absolutely no doubt.
Its lucy.
He can hear the frantic beat, but it's slowly fading away. She was in some sort of trouble... wait, weren't Gray and Happy with her? No Natsu can trust them without a doubt, Lucy has to be okay. She must be safe with them.
The slayer can't smell her, because he knows she's far but he realises that she's crying. His chest constricts painfully. What's happening?
Natsu wants nothing more than to go to Lucy, make sure she's alright. And not crying. Then hold her in his arms for as long as he can, as long as she allows him to. Because God, it has been too long.
But he also needs to defeat the man standing in front of him. Zeref Dragneel, the black wizard. And... his brother. Things aren't easy for Natsu. Never have been.
"Zeref!" The dragon slayer lunged forward, fists lit with flames of emotions. Natsu strikes again, he will, till he can convince himself that Lucy is just fine. His Lucy.
___
Lucy clutches her chest, there's a hot and burning sensation in her body and it slowly creeps into her heart. Molten markings all over her frame as she makes croaks in pain.
"Shit," Gray curses, applying more devil slayer magic onto Lucy's body. "My magic isn't working dammit!"
A tear escapes her eyes, the blonde barely smiles amidst the pain. "I've... fixed the... Natsu's book. He's not... E.N.D anymore..."
Happy cries in response, "Lucy! What's happening to you?!" His small paws rubbing her shoulder anxiously, the feline wails loudly. "Lucy!"
Gray leans her back on his side, gritting his teeth harshly as he continues to use his magic. The ice devil slayer doesn't give up, he pledges he won't. No way in hell, he can ever let his dear comrade die like that.
"Hang in there Lucy," he says. "Don't you dare die on us!" Lucy doesn't respond.
___
Natsu suddenly feels a surge of power within his brusied self. A warm, so soothing feeling settles inside his chest replacing the unwanted throb there. He's used to this sensation, it's the comfort Lucy radiates. He doesn't fail to recognise.
Of course it's because of her. She always manages to save his ass in time. No exception this time. His chest swells in pride. Such a girl she is.
But he can't feel her heartbeat anymore. He can't feel her, as if the connection was abruptly cut off. He swears he felt her presence a moment ago and now it's a void. Hollow.
The black haired man before him stares at the slayer with a sad expression.
"Everything comes with a cost, my brother Natsu."
Cost, Zeref said.
