One possible antagonist could be the Akatsuki members. They are always looking for strong opponents or valuable information. Maybe they target Iruka because they think he has some knowledge about Naruto that they can use, and Kakashi has to stop them.
In such a fanfiction, perhaps Kakashi might save Iruka from a dangerous enemy like Orochimaru's minions. Kakashi, with his Sharingan and powerful jutsu, could arrive just in time to fend off the attackers.
They are a popular pairing because they have a pre - existing relationship in the Naruto series. They are both important figures in the lives of the young ninjas. Kakashi is a respected and skilled jounin, and Iruka is a caring teacher. Their different personalities complement each other well. Kakashi is more reserved and mysterious, while Iruka is warm and open. This contrast makes for interesting storylines in fanfiction.
One common theme is the adjustment to married life. Since they are both ninjas, they have to get used to living with someone else in a more domestic setting.
One popular 'Kakashi and Iruka married fanfiction' is 'The Life They Built'. It shows their daily married life in Konoha, with some really cute interactions between them.
One great Kakashi and Iruka fanfiction is 'The Unspoken Bond'. It beautifully explores their friendship and how they support each other during difficult times in Konoha. Another one could be 'A New Beginning' which focuses on them working together to train the new generation of ninja. There are also some stories like 'Hidden Feelings' that hint at a deeper, more romantic connection between them in a really sweet way.
One popular Kakashi and Iruka lemon fanfiction might be 'The Hidden Feelings'. It delves deep into their relationship with some well - written emotional and romantic scenes. Another could be 'Unexpected Bonds' which shows their connection growing in a unique way. There's also 'Love Beyond the Village' that takes their relationship to different settings and situations.
One great fanfiction might be one where they go on a joint mission and discover new things about each other's pasts. It could explore their friendship and how they support each other during tough times.
Fanfiction.net is also a good place. There are many Naruto fanfictions there. Just use the search function and type in 'iruka and kakashi' to find relevant stories. However, the quality may vary, so you might need to browse through a few to find the good ones.
One common theme is the struggle between their human and vampire natures. They often have to deal with new instincts and powers while trying to hold on to their old selves. Another theme is the relationship aspect. Whether it's friendship turned into something more or a new bond formed because of their shared vampiric state.