Hermes rounded on Apollo as they left the throne room. "What's your problem, Apollo?"
The blond god stood his ground and folded his arms across his chest. "What problem?"
Hermes scowled. "What problem? The problem where you seem to hate Lucy now. What. Is. Your. Problem?" With each word, Hermes jabbed his brother in the chest.
Apollo glowered at him. "My problem, Hermes, is that she's not good for you." He stepped forward, forcing Hermes backward.
"How?" Hermes growled furiously. He brought his hand up and Apollo mirrored his movements. A sword appeared in Apollo's hand just as a caduceus appeared in Hermes'.
"She makes you weak, brother." Apollo shoved his sword forward and Hermes leaped back, metal clashing.
Apollo whirled around, thrusting his sword out and catching Hermes' arm. Hermes hissed and Apollo's lips curled up in a hard smirk. "She distracts you, making you weak. Every moment she spends alive is a danger to you."
Hermes narrowed his eyes, spinning his caduceus around to collide with Apollo's ribs with an audible crack. Apollo winced and limped backward, his hand pressed against the injury. "How much of this is objective, Apollo?"
"None of it, obviously. Were it to be objective, I wouldn't have told you at all because it's better for me to have your weakness pinpointed to exploit should I need to. I'm telling you this because you're my brother and I don't want you to get hurt again!" He healed as he spoke and rushed Hermes again.
Hermes threw him against the wall. "That's why? Not because of Cassandra, not at all?"
All emotion dropped from Apollo's face to be replaced with a flat, angry expression. "Don't bring that up, Hermes."
A cold smirk appeared on Hermes' face and he circled the god who hadn't bothered to get up. "No, this has nothing to do with Cassandra. The girl you wanted to protect so badly, and hurt so much. You're angry that I've protected Lucy better than you protected Cassandra."
Apollo flew over Hermes's head and grabbed his neck, holding his sword against his brother's throat. "Do not talk about Cassandra, Hermes," he hissed. "And if I remember correctly, you haven't done a much better job, since she's dead right now."
Hermes tensed. "I'm going to get her back."
Apollo laughed harshly. "Mortals never come back from the Underworld. Lucy's not going to be the first."
Hermes smashed his head against Apollo's face. When Apollo dropped his hands to cover his broken nose, Hermes whirled around and pointed his caduceus at his brother's chest. "She will," he snarled. "Just because you weren't clever enough to rescue Cassandra doesn't mean I'm not clever enough to rescue Lucy."
Apollo glared at his brother, wiping the golden blood away. "See what I mean? You never would have said any of that had it not been for your mortal. She's changed you."
Hermes dropped his caduceus and it disintegrated before it could hit the ground. "Maybe it's better that she did." He spun around, walking away.
He heard Apollo call, "I hope you're still my brother, Hermes."
Hermes clenched his fists and said nothing.
This is an interaction between Hermes and Apollo that I really wanted to put into the story, because it goes more into why Apollo doesn't like Lucy anymore, but it just never really fit. So here it is. :)