TOI! stands for twin on inside.
Used to describe two best friends who realize how similar on the inside they are, even though they look nothing alike on the outside. The ultimate fusion of one soul separated into two different bodies. People may become jealous of the power of the TOI! Yet no matter what, they stay strong. A TOI! may find that no matter what they say, do, wear and even think is similar to that of their TOI!
What oh my gosh, we're wearing the same dress! That's so TOI!