When Luca is first introduced in Heir of Fire, Celaena notes he looks to be at least a few years younger than her. He has a head of tawny curls and a tall frame with broad shoulders that he hasn't quite grown into yet.
He has a kind face and smiles broadly more often than not.
Luca is a very kind, almost naïve boy. He always appears rather eager to help with whatever needs to be done. In Heir of Fire, he is very kind to Celaena, even though he hardly knows her.
Luca is also very chatty, often talking to almost all the people who enter the kitchen, and he cares for pretty much everyone. When Celaena received a black eye during her scrap with Rowan, Luca looks worried and offers to get her some salve from his room, although he doesn't know her well and she's often been rather cold with him.
Luca is first seen when Celaena is brought to the kitchens in Mistward to help Emrys. He immediately greets Celaena and is very warm and happy, and talks constantly about his training and the sentries whom he admires.
Luca and Emrys tell Celaena what they know about Rowan when she asks, and Luca points out that he's very unkind and cold, even stating that he is "the meanest of Maeve's personal cabal of warriors."
When Rowan gives Celaena a black eye during training, he offers to help her, and continues to be kind to her whenever they work together in the kitchen. After Beltane, when Celaena almost burns out, Luca and Emrys even go to check on her and see if she's feeling better.
When Mistward is attacked by Adarlanian solders, Luca fights as well, and he was the one to inform Rowan that the scout leader Bas - who Luca greatly admired - was the one who betrayed them. After the battle, Luca and Emrys personally say good-bye to Celaena, and she offers both of them a place in her home in Terrasen for being such good friends.
After Heir of Fire, he is not seen again.