I wonder what this chicks end goal is, emotionally manipulate and toss away every woman she meets until they all hate her and she winds up alone forever? I’m just trying to understand the end goal

There is no end goal, she just does it for the love of the game.

But as others have been commenting already, I think and hope that with the other MC, this will backfire on her in the best way possible - her actually catching permanent genuine feelings.

And with the bar-owner friend getting more backstory but with no cliche loser flags so far, it'd be such karmic retribution if in the end Mashiro loses Chiaki during this "find your feelings" trial-run to relationships. Chiaki is liking what she has going on right now, but everything we've been show so far tells us she's not dependent on the relationship like Mashiro is (or is slowly becoming more so).

she's the one who was blocked 2 chapters ago by Mashiro.

Aha, thank you! I remembered that and was wondering since I couldn't remember the name, so you just saved me a dive!

https://dynasty-scans.com/chapters/ill_take_this_love_home_with_me_for_now_ch08#19
Called it right as i saw her lmao

That was a fun re-read.