"-desushi" mean "becase" and "and".

(I quote from episode 5.)

ふぉぉぉ！燃える展開です!! ちよりはバーニングチョリソーですしー!!

Wow, this is burning situation. Because chiyori is burning chorizo.

るぅ子さんがやらないなら私がやります ちよりがやりたいですしー！

If ruuko doen't play, I'll play. Because chiyori wan't to play.

The word "-desushi" itself is normal Japanese. But the overusing "-desushi" is a one of slang of young people.

In this anime, "-desushi" used for accent of character like -nyo.

"-desushi" mean "becase" and "and".

Let's take a look at a few quotes from episode 5 for example.

ふぉぉぉ！燃える展開です!! ちよりはバーニングチョリソーですしー!!

Wow! This is a burning development!! Because Chiyori is Burning Chorizo!!

るぅ子さんがやらないなら私がやります ちよりがやりたいですしー！

If Ruuko doesn't play, I'll play. Because Chiyori want to play!

The word "-desushi" itself is normal Japanese. But the overusing "-desushi" is part of slang of young people.

In this anime, "-desushi" is used for accent of character like "-nyo".