They both have big eyes due to the art style, but I guess the difference is, Mashiro has
Tareme Eyes which is a staple moe girl design element, while Emma has
Tsurime Eyes which are far more common with tsunderes. It doesn't help that she's got a single fang and twintails for a hairstyle...
It's only chapter 3 and we already have a sobbing losing heroine in Emma
For better or worse, Mashiro rekindled the rivalry keeping the love triangle alive.
"Or should we just leave oblivious Gentaro behind and go have fun ourselves?"
Emma was kidding, but these words appear to be awakening Mashiro to a reality that she's bisexual, if not just bicurious.
"I'm saying that even with girls, I still want to have some fun!"
Seems she's meeting, not beating the allegations. Not a bad thing, maybe we do need more bisexual heroines in love triangles. Sounds more fun to me, but maybe it's because I'm already tired of typical love triangles...