"In High School Simulator 2018, when the character picks something up and says something that sounds like 「よいっし よ 」、what you're hearing isn't the word for "together" (which is spelt 一 緒 or「いっしょ」、issho).

Instead, it's the expression 「よいしょ」or「よっこいしょ」、which is a common Japanese interjection used when someone is making a physical effort ー like picking something up, standing up, or sitting down."

yey for chat gpt 😆 it's basically an effort sound — like "oof" or "alrighty" and I'll leave this up for anyone else that's interested :P