extemporaneous (adjective)

1. The painter created an extemporaneous masterpiece in just a few hours, using a variety of bright colors and bold strokes.

2. The comedian didn't have any prepared material, so he had to come up with an extemporaneous joke on the spot, which ended up being hilarious.

3. The architect decided to design an extemporaneous outdoor seating area that complemented the existing building, without any prior planning or sketches.

4. The anime character made an extemporaneous decision to save a fellow character from danger, showing courage and quick thinking in a critical moment.