I actually really like Akira so much more as a character after this chapter. We've seen her be a bit jealous before now, but she was still a mostly bland character imo but I enjoyed these ugly characteristics. Her feelings are certainly not positive and her ego certainly needs some work, but that's what I find appealing about it. She's a character that needs a lot of growth and change.
She needs to understand that Mayuki has grown up and isn't still that little girl she needs to protect. She needs to understand that she isn't "better" than Mayuki. She needs to come to understand why Rin likes Mayuki and what those feelings actually mean. She needs to get her jealousy and feelings under control. There's just so much room for great character development and if done well then I see it really strengthening the polycule as a whole.
If done well being the most important part. Rin and Mayuki have already built up a great dynamic. They're fluffy and sweet and those kiss scenes are so saucy! (Seriously, this manga has some of my favorite kiss scenes at the moment.) They're everything you really want in a yuri couple and they could probably pull off their own manga as a monogamous pairing. So, the introduction of Akira needs to feel like it adds to the relationship between all three characters rather than distracts from the relationship between Rin and Mayuki.
I'm looking forward to seeing how Akira changes the dynamic between these characters when she becomes more involved in the romance. I have hope and trust that that mangaka will be able to pull it off in a satisfying way.