I wonder where Koichi and the others went.
Those gangs are all Viet's sworn brethren.
Aren’t you still minors?
You'll see this attached to other words to make them plural. That's why it's called a pluralizing suffix.
This is almost the same reading you learned with the kanji. Remember たつ? Well this is read たち. Here's a mnemonic to help you remember it:
If you want to pluralize something, touch (たち) it to something else. One egg touches another egg, well now they're eggs. Plural eggs! One friend? No. Touch them! Touch them right on the face. Now there are two friends. Plural friends! Thanks to the good ol' pluralizing suffix touch!
Oh, and don't type the 〜 out when writing the answer. It's just there to let you know that there's usually something attached to this word.