I saw this Headcanon and mostly based this one off of it.
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Nico's Approval
Frank was worried.
Nico was hanging out with them. Well... everyone was, but Nico worried Frank the most.
Hazel was at ease as usual having no problem with her big brother. Frank knew that Nico didn't completely hate him he figured hat out years ago, after the whole corn plant incident. But we don't talk about that.
But Frank and Hazel haven't told anyone about their recent engagement. Frank couldn't help but wonder what Nico would do. They were all adults... sort of... Frank was now 25 and Hazel 22. They had been dating long enough. So Nico would have no grounds to kill him right? Other than Frank being with his younger sister... is that-
"Are you ready to go or not?" Hazel call waiting at the door of their apartment. Frank buries his worries (for now) and follows his fiancé out the door.
~~~~
"Frazel is finally here!"
Frank holds back an eye roll. Hazel gives a laugh.
"Percy they each have their own names," Annabeth sighs.
"Shh. They're my OTP," Percy says turning to the couple.
"When did Percy become a Fangirl?" Leo asks.
"He's always been that way," Piper says.
"More importantly," Annabeth states. "Did you just tell me to 'Shh'!"
Percy gives her an uneasy smile. "I love you?"
Annabeth shakes her head.
"So what are we doing? I say we get food!" Leo shouts earning a facepalm from Calypso.
"Food sounds good," Thalia comments.
The others nod in agreement..
"Wait, where's Nico?" Hazel asks.
"He said he'll meet us later. Underworld stuff," Jason says.
Frank internally thanks every god he can think off.
The large group heads to a restaurant and sit at the giant booth.
Frank looks around at everyone: Percy, Annabeth, Jason, Piper, Thalia, Leo, Calypso, Hazel and himself with Nico coming later. Or hopefully not at all.
"Oh my gods!" Frank is brought out his thoughts as Percy shouts. His eyes are open wide as he reaches forward grabbing Hazel's hand examining it.
"Congrats!"
The other group repeats it as Frank is blushing so much he tries not to change into an animal in the restaurant.
~~~~
"Why do they go in packs?" Leo asks as the girls walk off to the bathroom.
"No one knows," Jason answers.
Percy shrugs. "According to Annabeth its because Hermione was attacked by a troll."
The other boys give him looks which he ignores.
"Hey Frank," Leo says changing the subject. "think that girl is staring at you."
"I swear if you make Zhang dump my sister, I will slaughter you and make sure your comfortable in the Fields of Punishment." A voice growls. Frank turns around to see the son of Hades who has a lethal glare- not his face the other one- and his arms crossed.
"Hey... Nico..." Leo gives a nervous laugh and steps behind Jason. "Hide me."
"I doubt he's gonna dump her," Percy says. "They're engaged now."
Nico blinks. "Finally."
"W-What?" Frank stutters confused.
"Finally," Nico repeats pulling some fries out of his McDonalds. "You two have been dating forever and you live together. I would certainly hope it wouldn't all be for nothing and you dump her."
"Hey Nico!" Hazel shouts as she grabs him in a hug.
Nico chuckles. "Congrats. Zhang's a good guy."
As everyone talks Frank can't help but smile. He had thought Nico would kill him. But apparently he had won Nico's approval.
Now the next problem: Hazel had suggested Percy or Nico as the best man....