I think everyone r being a little too harsh on Niki to judge who Akira loves more. She started really really late and has a huge disadvantages. While Ayane and Maya appeared from the beginning and later became a part of "End of the world" team. Three of them especially Maya and Akira spent alot time together to go through this "End of the world" thing, a special situation that no normal people could experience. So all of that give Maya Prime, Ayane, Akira have a special relationship together without the need of pre-amnesia memories.
For Niki, I kinda understand why everyone said shes gonna need full-memory Akira in order to be on par with Maya Prime. She doesnt experience the "End of the world" with Akira, guide him through it or anything special. Shes a real normal person at the end of the day, all she could do r being there for him, guide him through rough times and assure a safe place for him. Which is pretty much not that special compare to other girls. Shes only shine the moments past memories come back and Akira feel something click in his heart such as back when he first read Niki's letter or in "Glasswalker".
I still stand with my points, 16 events only for Niki and the first 6 probably only a set-up for Glasswalker. Sel r holding Niki back really hard at the moment. I just wish that Niki will have special memories with Akira at the current time same as Maya so that she wont rely on memories anymore. Because if all the memories come back to Akira, theres no "on par with Maya Prime", thats gonna be a huge sweep for Niki, mark my wordddssss.
Edit: oh I forgot, Akira push Niki away most of the times because shes too good for him and doesnt want her to suffer more because of him too.
And she also spend much less time with Akira than other students of him too. Shes an adult, has a job and apparently in the "side girl" section... Fuck