Even though Nezuko is listed as a mid-game boss in Project Slayers, she can be very challenging as her Blood Explosion Demon Art is arguably the most powerful one in the game, allowing her to deliver devastating combos. You can check our Project Slayers map for her location in Dangerous Woods, but using the Horse Guy to Fast Travel to her is recommended.
Fighting Nezuko unprepared makes her look really hard, but there is a simple solution to take her out fairly easily by taking advantage of her Speed Rush ability. Basically, you have to block her rush ability and if you timing is perfect (it's fairly easy to get it right), you will leave her stunned and ready to be comboed.
Even if you timing is not perfect you will still block her attack. In the moments before she starts her normal attack combo start slashing her with you own normal attack combo until you know her down.
However, note that after you block her rushing attack, if you don't stun her, Nezuko will be slightly behind you so you really need to adjust your position fast to get the hits in before she starts her normal attack combo.
Once she gets back up she will attack with her speed rush again. Block it and keep repeating the process until you take her down. Depending on your level and mastery doing this 2-4 times should be enough.
Finally, even at +5 block you won't be able to fully guard against her normal attack, which seems to deliver 6 hits, so try to avoid that if you don't want to have your guard broken.
In the video guide below the fight starts at the 1:50 mark.
Conclusion
While you are here, don't forget to check our Blood Demon Art Tier List, Breathing Tier List, and Weapon Tier List to set up your character for success in the game properly! We also have guides on how to get Water Breathing, Thunder Breathing, Insect Breathing, or Wind Breathing.
Finally, note that a private server will make your life easier while leveling up.