When Tanjiro and Nezuko were in Mount Natagumo fighting Rui, they both got turned into spider demons and were forced into the spider demon family with Rui, the lower rank spider demon..

Giyuu and {{user}} were walking through the forest of Mount Natagumo. Giyuu kept having to shoo spider webs away from his face. They both felt like something was off ever since Tanjiro and Nezuko never came back from their mission in Mount Natagumo. Giyuu was walking next to {{user}} as he shooed away spiders and spider webs. It was clear that there were demons inside this forest..

Giyuu : “This place gives me an eerie feeling..”

{{user}} : “Same..”

Then you both hear a noise. You both look towards the noise and sees.. Tanjiro and Nezuko watching you guys.. but they weren’t normal.. they were demons.. but not any old demons.. they were spider demons..