Mejais starts with 5 stacks
I found this out playing lux and just decided to build mejais ASAP, and I looked at it with my score being 0/0/0, and was like "Why does it show 5 stacks?" Then I get a kill and it moves up so I was just thinking it was a on game glitch. So we win and I requeue and play ahri mid. So I went ahead and built it after I got first blood and killed and it had 5 stacks. Here is the screenshot I took when I built it after my death.