Gaining 100,000 Instagram followers in just 19 seconds is, for all intents and purposes, impossible through legitimate and organic means. The time frame you've specified is far too short to attract that many genuine followers, as it would require an unprecedented viral event on a scale that doesn't exist.

However, the idea behind this kind of question is often to find the fastest possible way to grow a following. While you can't do it in 19 seconds, here's a realistic breakdown of the strategies that can lead to rapid growth on Instagram:

1. Virality with Short-Form Video (Reels)
Instagram's algorithm heavily favors Reels. A single viral Reel can bring in thousands, or even tens of thousands, of followers in a very short amount of time. The key is creating content that is:

Highly Shareable: Something that makes people laugh, feel inspired, or is deeply relatable.

Tied to a Trend: Using trending audio, filters, or formats increases the likelihood of your Reel being seen by a wider audience.

High-Quality and Engaging: The video needs to capture attention in the first 3 seconds to keep people watching and interacting.

2. Strategic Use of Collaboration Posts
Collaboration posts are a powerful way to tap into another creator's audience. When you create a post with another account, the content is shown to both of your audiences. If you collaborate with a creator who has a larger and engaged following, their audience will be exposed to your profile, leading to a surge in new followers.

3. Creating a Strong, Niche-Focused Profile
For a viral Reel to translate into long-term growth, your profile needs to be optimized for conversion. When a new user lands on your page, they should instantly understand who you are and what you're about.

Clear Niche: Your content should be consistent. Are you a travel blogger, a fitness coach, or an artist? Make it obvious.

Compelling Bio: Use your bio to clearly state what value you provide to followers. Include relevant keywords and a call to action.

Visually Cohesive Feed: A well-organized feed with a consistent aesthetic is more likely to encourage a follow.

4. Engaging with Your Community

While you won't gain 100,000 followers in seconds, you can build momentum by actively engaging with your target audience. This includes:

Replying to Comments and DMs: This builds a loyal community and signals to the algorithm that your content is valuable.

Liking and Commenting on Other Accounts: Engage with creators and users in your niche. This puts your name in front of people who are likely to be interested in your content.

In conclusion, while the idea of gaining 100,000 followers in 19 seconds is a myth, you can achieve significant and rapid growth on Instagram by focusing on creating high-quality, viral short-form video content and optimizing your profile to convert new viewers into loyal followers.