I finally got Seirios yesterday! I have to say, I was concerned when I saw that some of the mini album tracks were on the album, but I shouldn't have been worried. RURUTIA makes it flow together as though those tracks were made for this album.
Seirios the song is an amazing album opener as usual, it grabs your attention right off the bat. The soft and fast paced verses of Silent Prayer are really awesome! I was surprised when it took on an upbeat sound for the chorus, in a good way of course. Opus fits in nicely (I wonder if the mini albums were sort of like maxi singles - both Opus and Hyousa made the cut). Aurora Hikkou has such a nice mysterious air and they lyrics contain truly beautiful imagery. Aurora Hikkou thankfully also breaks up Opus and Ryuukou, since they appeared together on a mini-album. Ryuukou has a nice poppy sound before leading into the love ballad Muyuuka. Muyuuka is nice, but one of her more forgettable songs in my opinion since it fits typical Jpop patterns. LAST DAY is a beautiful piano driven song, but falls in a similar category as Muyuuka for me. Hyousa was released before, but I still love it, the chorus really grabs me. Yume Hotaru is great with lots of layered sounds and again really beautiful imagery. The guitar bridge is nice too; very subtle. VOID makes use of a music box - it sounds great with good headphones, but it puts me to sleep on regular speakers!

VOID sounds like it could have been the last track but we still have Hoshi to Hane which is a beautiful atmospheric track again using a music box and RURUTIA's layered vocals. I got a nice surprise when the piano came in though! I love the sound of a crackly record that is added to the track.
My favorite tracks are Seirios, Silent Prayer, Yume Hotaru, and Hoshi to Hane. (Excluding the 4 previously released tracks!)