The sister is still the most overly fucking annoying character here, there is nothing about her that is redeeming except for her skill to be an event trigger for the mc
If you've been around long enough you know on instinct that the Senpai route is gonna crash and burn and our guy won't even notice it. Pretty typical but still sad.
Still don't give a flying fuck for their romance at all as in why the hell is it even there except to give the writer an out so he can throw these disposable characters away after giving Rimuru a reason to go demon lord
The amount of character growth while cringey at times is amazing in this manga and if you really invest in it the emotional fulfillment in the later chapters is absolutely worth reading. I highly recommend this because it is the epitome of sweet and wholesome.