Well I improvised a bit and it worked for me, although it required me more retries than I would've liked (T_T).
So let me explain it in steps :
1) I noticed that for reaching below 30 willpower, my corruption stat should be zero. And for further pink scenes I had to consume 1x Blessed Water before initiating the fight.
2) While initiating the fight with the Mutated Spore, I always removed the collar at the very start. However later I realized that it didn't work. So I waited until I reached 40 willpower in the normal state and after that I removed the collar and got my willpower till 20 which was the limit I guess (Because even after 100's of tries it never went below 20)
NOTE: You shouldn't regenerate your HP during this as it would just be wasting your Apples, just try to reload your save before the fight and try again if willpower doesn't go till 40 in normal state.
3) After defeating the enemy and collecting the items, I returned to Trademond and sold the collected Star Metal. I then gave the ingredients to the Alchemist:
2x Ether and 1x Mutated Spore.
Doing this gave me a 10% Discount on the items and then I bought 1xVitality Potion from him. I used this potion before asking him for a Discount(Lewd Scene).
4) After the lewd scene I bought 2x Mana Stones and 2x Vitality Potions. So in total I had to buy 3x Vitality Potions : 1 with 10% Discount, while 2 with added 40% Discount. (In walkthrough there were only 2 Vitality Potions mentioned)
After that, I followed the walkthrough while consuming 1 Vitality Potion before each scene on the day, and was able to get the pink versions for all of them. So it kind of worked for me..
I'm currently at Day 22, so if I further encounter any such things I'll inform them here. I request dev to fix this bug if possible, It will be very much appreciated. I hope this helps so please let me know if it works for you. Have a good day everyone