Yet Another Strategy with Camus (Hard, Lunatic, Infernal)

For Hard, Lunatic, and Infernal.
Eldigan and Cecilia are replaceable. The one unit really needed is Camus with Vantage, and to a lesser extent Reinhardt with Lancebreaker. Cecilia and Eldigan supply Fortify and Hone Cavalry respectively. Eldigan can be replaced with any (horse unit ideally) that can take out a weakened Cecilia, so just about anyone. Cecilia can be anyone.

*On Hard, Camus baits Cecilia, Lance Cavalier, and Lilina by moving into nearest red space. He can kill all of them on response. On the next turn, he can also handle the Lance Flier, and Reinhardt handles the Bow Cavalier.

*On Lunatic and Infernal, instead break the wall in front. Use Reinhardt to quickly take out the Lance Flier and have Camus use Reposition to get him back to safety, leaving Camus in the danger zone. Camus can take the subsequent attacks from Cecilia and Lilina, killing Lilina with Vantage and Bonfire. Next turn, Eldigan can finish off Cecilia and Reinhardt can take out the Lance Cavalier. Next turn, Reinhardt takes out the Red Infantry Mage (Infernal only), Eldigan chips at the Bow Cavalier and Cecilia uses Reposition to get Camus in range to finish it off.

Necessary/helpful skills:
5* Camus:
Reposition
Bonfire
Fury 3
Vantage 2
Goad Cavalry

5* Reinhardt:
Luna
Death Blow 3
Lancebreaker 1
Ward Cavalry

5* Eldigan:
Hone Cavalry

4* Cecilia:
Reposition
Fortify Cavalry

I have a -ATK Reinhardt and a 4* unbuilt Cecilia, this strategy's pretty flexible.

Camus

Reinhardt

Eldigan

Cecilia