One possibility could be that the Molecule Man's powers somehow disrupt the magic in the Harry Potter universe. Maybe he accidentally alters the molecular structure of Hogwarts, causing chaos among the students and teachers. Harry and his friends would then have to figure out how to reverse the changes and send the Molecule Man back to his own dimension.
The main antagonist could be an evil version of the Molecule Man. Maybe in his own dimension, he was corrupted by power and when he enters the Harry Potter universe, he wants to take over there as well. He would use his molecular manipulation powers to create all sorts of disasters, like turning the Forbidden Forest into a deadly, mutated place. Harry and his friends, along with the good - natured Molecule Man, would have to fight against this evil version.
One example could be a story where a single molecule is found in outer space that has the ability to terraform planets on its own. Another could be a scenario where a single molecule is used as a weapon that can dissolve any material it comes into contact with.
Single molecule science fiction could be about the potential of a single molecule having extraordinary capabilities. For example, a single molecule that can power a small device indefinitely. It might also involve the idea of a molecule being sentient or having the ability to transform matter at a microscopic level.
A water molecule might start its day in a large body of water like an ocean. It is constantly moving and interacting with other molecules. It could be part of a wave, crashing onto the shore. Then, as the sun comes out, some of it might evaporate and turn into vapor, rising up into the atmosphere.
A first person water molecule story could be about the journey of a water molecule. Maybe it starts in a cloud, feeling the coolness and the company of other molecules. Then it falls as rain, experiencing the rush through the air.
Well, the life of a water molecule is a journey. In its liquid state, it has hydrogen bonds with neighboring molecules, which give water its unique properties such as high surface tension. As it moves through the water cycle, it changes forms. When it evaporates, it breaks free from the liquid and becomes a gas. In the atmosphere, it can combine with other substances and then return to Earth in various ways, either soaking into the ground or running off into rivers again.
The main events start with the water molecule being in a liquid phase, for example in a lake. It gains enough energy and changes to a gaseous state through evaporation. In the atmosphere, it combines with other water molecules during condensation to form clouds. After that, precipitation occurs and the water molecule returns to the Earth's surface. It may then be part of a runoff, seep into the ground, or be used by living organisms before starting the cycle anew.