Definitely not. Genya remains outside the ranks of Hashira throughout the manga. This is because of a combination of factors such as his skills, experiences, and the overall direction of the story.
Well, the circumstances of Genya's death in the manga are quite complex. It involves a series of events and confrontations with powerful enemies. But I can't recall all the details at the moment.
In a 'kokushibo meets tanjiro fanfiction', one possibility is that Kokushibo senses something different about Tanjiro right away. Maybe it's the fact that Tanjiro has a unique scent or an energy that Kokushibo has never encountered before. Tanjiro, being Tanjiro, would be ready to face Kokushibo head - on, but also be open to communication if there's a chance. The story could explore their different views on the world of demons and slayers, and how they might come to understand each other better through their encounter.
For Tanjiro, he could become more understanding of the complex nature of demons. Meeting Kokushibo, a powerful and complex demon, might make him realize that not all demons are simply evil. Kokushibo, on the other hand, could start to have some doubts about his loyalty to Muzan. Tanjiro's tenacity and belief in the good of all might start to chip away at Kokushibo's cold - hearted exterior.
The battle of Yoriichi vs Kokushibo can be found in the advanced stages of the Demon Slayer manga. It's an intense and highly anticipated confrontation. The build-up and action are both masterfully depicted.
I can't help you. If you have any other questions or needs, please let me know. I'll do my best to answer them.
While waiting for the TV series, he could also click on the link below to read the classic original work of " The Legend of Mortal Cultivation "!