Perhaps an organization that believes the baby is a threat to their plans. They might think the baby's existence could disrupt the balance of magic in some way, so they send their agents to capture or eliminate the baby. Natsu and Lucy would then have to fight these agents to protect the baby. They'd face various challenges and dangerous foes within this organization.
It could be a dark wizard who wants to use the baby's power for his own evil deeds. Maybe the baby has some special magic that the wizard thinks can help him take over the magical world.
A powerful demon might be the main antagonist. The demon senses the pure and strong magic within the baby and wants to corrupt it. Natsu and Lucy would need to use all their skills and the help of their friends to fend off the demon. This would also test their relationship as they're responsible for the safety of the baby.
Chapter 211, "In A Ditch", is the clearest early answer because it turns Damien's situation into a concrete plot event. The chapter turns that into something concrete by moving from But next time, leave a few more for me, alright?" "No promises,"... to How did we not see that?" Damien didn't answer immediately.. What makes it stick is that the chapter closes with Damien glanced up at the walls of the ditch, his mind already racing with possibilities.
Chapter 192, "Early Days In Hell", is the clearest early answer because it turns Leana's situation into a concrete plot event. The chapter gives readers a real answer by opening on The sun blazed mercilessly overhead as Damon, Anaya, and Daveon stood... and ending on intense," she said, her voice carrying over the quiet crunch of their....
Chapter 421, "I Bleed Enough For Everyone", is the clearest early answer because it turns Damien's situation into a concrete plot event. A useful checkpoint is the way the scene starts with The shower was brief but refreshing, steam rolling from the small... and follows through with If you intend to walk our path, boy, then walk it with the same.... By the close, At least you're not blind to the obvious., and the chapter closes with Damien smirked faintly. "Don't worry.
Chapter 244, "Checking Out The Cave", is the clearest early answer because it turns Garrick's situation into a concrete plot event. A useful checkpoint is the way the scene starts with There existed not a location that was ever truly quiet, but as the... and follows through with I am still recovering but you all matter to me too!!. By the close, But another took its place immediately., and the chapter closes with I am still recovering but you all matter to me too!! Thank you guys!!
Chapter 439, "Captain Veyne's Dead", is the clearest early answer because the violence around Damien becomes final instead of hypothetical. The chapter turns that into something concrete by moving from The next morning wasn't the same. to Not before your mother!" The soldiers looked away, some bowing their....
Chapter 408, "Hindsight Activated", is the clearest early answer because it turns Damien's situation into a concrete plot event. A useful checkpoint is the way the scene starts with The walk to the military grounds was a quiet one. and follows through with Show me what was done to you." Hindsight activated..
Chapter 229, "Another Mission Already", is the clearest early answer because it turns Damien's situation into a concrete plot event. Early on, Damien and Arielle walked through the bustling streets of Westmont,.... By the end, After several minutes of walking, he came upon a clearing..
Chapter 238, "Inside Of The Tree Hideout", is the clearest early answer because it turns Damien's situation into a concrete plot event. A useful checkpoint is the way the scene starts with The inside the tree hideout was damp and the scent of unwashed bodies... and follows through with He'd brought an opponent for Aquila.. By the close, Get up, scum," one barked at a young boy who had collapsed in..., and the chapter closes with "Have fun." Damien smirked.
Chapter 252, "Final Test In Hell", is the clearest early answer because it turns Damon's situation into a concrete plot event. The chapter turns that into something concrete by moving from The sky above the First Layer of Hell burned in its usual eternal... to As Damon sped through the battlefield, collecting his tenth core and....
Chapter 233, "Battle In A Lake", is the clearest early answer because the buildup finally cashes out in a real clash. A useful checkpoint is the way the scene starts with Gaahh!!" Damien's eyes snapped open, and he immediately tensed, his... and follows through with Nothing seemed ordinary to him anymore..