There are many on Fanfiction.net as well. A lot of the fanfictions in this pairing play around with their different personalities. Bucky's brooding nature and Darcy's sassy and intelligent self make for an interesting dynamic. You might find some fics where they are paired up on a mission together and that's where their relationship starts to develop.
Sure! You can check out Archive of Our Own (AO3). There are numerous Bucky Barnes x Darcy Lewis fanfictions there. Some popular ones often involve them getting to know each other in different post - battle scenarios. For example, in some fics, Bucky is adjusting to modern life and Darcy helps him with that while they develop feelings for each other.
Another place to look is Tumblr. Some users post short but sweet Bucky Barnes x Darcy Lewis fanfiction snippets or link to longer works. Some of these works explore how their relationship could develop in the context of the larger Marvel universe, like how they deal with other superheroes and villains while falling in love.
Chapter 859, "I Bet She Won't Last Ten Minutes!", is the clearest early answer because it turns Shuiyun Mountain's situation into a concrete plot event. It opens with All morning, the two little ones were quiet, not making a peep, even...
Chapter 631, "It's Him Who Got Hurt, Then It's Fine", is the clearest early answer because it turns Jiang Li's situation into a concrete plot event.
Chapter 698, "Brother Yan Was Just Forced!", is the clearest early answer because it turns Jiang Li's situation into a concrete plot event. The chapter turns that into something concrete by moving from Jiang Li immediately asked for some tools and colored paints.
A practical answer is Chapter 3, because it turns the idea into a concrete scene. The chapter opens with Qiao was still annoyed at the attitude of this unknown girl when she heard..., adds pressure through So without a second thought, she blurted out a fierce challenge, "Fine, if..., and ends on.
Chapter 12 is the strongest chapter-level answer because it starts from Qin?" Jiang Li called out twice, and only then did Mrs. and follows through on The glass shattered on the floor with a crash, attracting the attention of....
Chapter 505, ""Postpartum Care for Sows", is the clearest early answer because it turns Shang Shaobai's situation into a concrete plot event.
Chapter 852, "Could That Be an Aphrodisiac Spell?", is the clearest early answer because it turns Rong Junsheng's situation into a concrete plot event. It opens with Rong Junsheng's words startled Shi Lei and Rong Kexi.
Chapter 754, "Evil Can Never Defeat Justice", is the clearest early answer because it turns Fang Wenzhe's situation into a concrete plot event. The chapter gives readers a real answer by opening on After the court trial ended, everyone immediately threw a party for...
Chapter 565, "Our Homeroom Teacher Isn't As Twisted As You!", is the clearest early answer because it turns Ai Xiaochun's situation into a concrete plot event. A useful checkpoint is the way the scene starts with After the ingredients were delivered, Chen Manman handed them all...
Chapter 885, "Isn't This Wine?", is the clearest early answer because it turns Isn's situation into a concrete plot event. The chapter turns that into something concrete by moving from Daoist Shuiyun's words weighed heavily on Jiang Li's heart like a...