Gonna write some headcanons for my darling Iris & her family
1. Age 5-10
She first knew about Noctis was from Clarus, he talked about this shy and kindhearted kid and that made Iris had a good impression even before she met Noctis in person.
After the incident in BH3, she was allowed to tag along with Clarus or Gladio sometimes and got the chance to play with Noctis. Iris was a bit upset when she found out she could not go to the same school with Noctis. (she went to another private school instead)
When Iris was 6, Gladio took her to the amusement park cuz Clarus couldn't make it even though he promised. Gladio carried Iris on his shoulder like other parents did, Iris was excited at first, and then Gladio was scolded by other tourists who mistook them as father and daughter
Gladio was considered too young to have a kid of his own (he looked like 22 at the time), although they tried to explain, that still left bad memories for Iris. Since then Iris refused to go out with Gladio alone and started to be picky about her brother.
Things actually got worse from Gladio's point of view when Ignis stepped into his life, because Iris made clear statement that she wish Ignis could be her brother (who wouldn't!!). But Gladio wouldn't argue with Ignis about this.
Gladio was a little bit worried when he thought his little sister fell in love with his best friend. Ignis knew that Iris's heart was fixed on Noctis so he told Gladio not to worry. Iris was more interested in the royal desserts that Ignis brought to her and news about Noctis.
From Iris's perspective, Gladio and Ignis are friends for life. She was also the main victim who had to endure Gladio's endless praise of Ignis. (Clarus was not at home that often) She knew her brother likes Ignis (who doesn't?!) but wasn't aware of the struggle Gladio faced.
When Ignis (17) & Gladio (18) were still hesitating about their true feelings to each other, Iris gave Ignis a push (without realizing what she actually did). I wrote the process here, feel free to check it out.
2. Age 11-15 (before Insomnia fell)
Clarus discussed with Gladio and decided to let Iris have more freedom. So she get to choose the school she want to attend, and learn any skills she was interested in.
Clarus wanted his little daughter to be happy. They decided not to let Iris carry the load of the family and Gladio promised that he will take on responsibilities promptly.
A lot of things happened when Iris turned 13. Gladio came back from a festival and showed his tattoo. (hc for the true meaning of this pls check https://twitter.com/anpathio/status/1330530194302459904) She immediately cried to Clarus that Gladio had become a primitive.
Iris "I don't care! A person who likes to live in the wild, knows how to drill wood for fire and with tattoo is a primitive! "
Noctis turned 18 in August, a royal ball was held in his honor. (https://twitter.com/anpathio/status/1337820417659076610)
With Gladio's help, Iris was Noctis's date that night and the two had an opening dance together. A dream came true for Iris
While staying in Lestallum, she came across a secret fan club of "Captain Gran", the ladies had tons of photos of Gladio and Ignis. She was a bit shocked knowing that her brother was actually quite popular among hunters (both men & women).
She still loves Noctis after nearly 20 years. She is devoted to the one she picked, just like her father and brother. Clarus served Regis all his life, Gladio and Ignis were together for at least 20 years. I think Amicitia family members are all stubborn about love.
In my fanfic, she kept teasing Gladio as a way of getting her old life back and Gladio as always tolerate her. She was never really worried for her brother or other party members until incidents in Altissia.
4. Episode Hilian
Hilian is a character I designed in comrades and he would be interacting with main characters (Gladio, Ignis, Iris, & Cor) throughout the 10 years.
I plan to start this fic when I finished my current work "Long road toward the Light" (almost done)
One event took place at Year 4 (M.E.760), when Iris was 19. The Kingsglaive still had several strongholds in Insomnia, and Iris was appointed as team leader in a mission that went south.
She made a bad judgement and although all team members got out alive, some of them were badly wounded including herself and Hilian. Gladio came to visit her with a serious look and asked Hilian to leave the room. He tried to defend Iris and yet only got Gladio's apology to him.
Iris thought she would be scolded by Gladio but he said that he's glad Iris is still alive. And that he already talked to Cor and got permission: Iris would be sent back to Lestallum to recover and stay there as logistic support.
It took a few moments before Iris realized that it meant she had to leave. She was angry and questioned Gladio that why couldn't she stay and take responsibilities as a leader? "You've made mistakes before, so why should I back out? I am capable of being in the frontline."
Gladio "I'm sure you are capable. That's why you were stationed here for the past 2 years. I am not asking you to back out from anything, I am simply begging you to stay safe in Lestallum. This is also a request from leader of House Amicitia."
Gladio sincerely apologized to Iris, for he had already decided that his lifelong partner would be Ignis, and he would only be responsible for Noctis's future (the only "child" they would ever have).
Gladio wished the spirit and all the merits pass down from Clarus should continue, the Amicitia line cannot be broken. "I am sorry you have to bear this responsibility, please try to understand."
Iris knew what it meant. Gladio thought he and Ignis might perish in the line of their duties, and they were ready for it. Along the way, her big brother had already taken tons of responsibility, and now it's her turn. "You are too cunning, brother/ずるいよ お兄ちゃん"
I said in other thread before that Hilian is kind of like Gladio & Ignis's son (I may explain his origin when I start to write it). But as much as I want it to happen, Hilian would not be adopted by them. After 9 years, Iris would be the only one who remember his presence.