Seishitsu is a Japanese word that means "personality" or "character." It's like the things that make you who you are, like your interests, your likes and dislikes, and the way you act around other people.
Think about your favorite character in a book or movie. They probably have a really strong seishitsu that makes them unique and interesting. Maybe they're brave and always stand up for what they believe in, or maybe they're funny and like to make people laugh.
Just like people, every object in the world has its own seishitsu. For example, a tree might be strong and tall, with lots of leaves that rustle in the wind. A rock might be hard and heavy, with rough edges and interesting colors.
So when you hear the word seishitsu, just think about the unique qualities that make things special and interesting. Whether it's a person, an animal, or even an object, there's always something that makes it stand out and be different from everything else.