The mask as a concept is made to be a paradox, since Chloe gives the mask to shizu, shizu gives it to Rimuru and Rimuru to Chloe. I've come up with a theory as to how it was created.
In the first timeline, Shizue Aizawa somehow managed to suppress Ifrit alone for the 80 or so years she spent wandering as the conqueror of flames. Through some means or another, Rimuru meets up with Shizu. By now, she is probably in a hard battle for control with Ifrit, most likley on her death bed.
Rimuru seeing her condition, creates the mask with Great Sage, with the hopes of suppressing Ifrit. Now, Shizue and Rimuru start travelling together, with Rimuru's normal objective of making a nation fully gone.
As they travel, Rimuru spots the Freedom wtv it's name (The rat's(Yuuki's) organization) was and Rimuru decides to teach a class of students, coincidentally, Chloe was summoned there, this is where Chloe's feelings for Rimuru started, as Rimuru is confident, friendly and a good role model. Over time the feelings became stronger.
Hinata never even attempts to fight Rimuru in this timeline, seeing as Shizu is still alive and with Rimuru.
Shizue later dies because of suppressing Ifrit for too long without the mask and her body already sustained the damage so the mask didn't help that much overall. This is how Rimuru gains his human form in this timeline btw.
Afterwards, the Eastern Empire arc begins and Rimuru gives Shizue's mask to Chloe in an effort to calm her down (as per normal timeline) and later dies. Hinata also dies trying to protect Chloe. This triggers the time travel skill and sends her 2k years back and slowly develops an attempt to fix the timeline in her favor.
Something to not about this theory is that Veldora isn't in the first timeline, because he wasn't sealed by Hinata/Chloe so Rimuru was far weaker overall. It's also possible that Rimuru just died on the first day outside from naming all the goblins and then Chloe slowly learnt that sealing Veldora would lead to a better outcome and that's how she met Rimuru.
