In your collection, some of the songs have HD or MX or RD style for 4B. However, you will need to play that song on Normal if you want to get it. For most MX and RD songs, it is unlocked through playcount.

Song style	How to unlock
Beat U Down MX	Play 515 Songs.
Dear My Lady HD	Clear "Dear My Lady" NM 4B Style.
Desperado HD	Clear "Desperado" NM 4B Style.
DJMAX HD	Clear "DJMAX" NM 4B Style.
Fury HD	Clear "Fury" NM 4B Style.
Get Up HD	Clear "Get Up" NM 4B Style.
Heart Of Witch MX	Play 220 Songs.
Higher HD	Clear "Higher" NM 4B Style.
Honeymoon HD	Clear "Honeymoon" NM 4B Style.
Honeymoon RD	Play 105 Songs.
I Want You HD	Clear "I Want You" NM 4B Style.
In My Dream HD	Clear "In My Dream" NM 4B Style.
Keys To The World HD	Clear "Keys To The World" NM 4B Style.
Lover HD	Clear "Lover" NM 4B Style.
Melody HD	Clear "Melody" NM 4B Style.
PDM HD	Clear "PDM" NM 4B Style.
Play The Future HD	Clear "Play The Future" NM 4B Style.
Ready Now HD	Clear "Ready Now" NM 4B Style.
Remember HD	Clear "Remember" NM 4B Style.
Ruti'n HD	Clear "Ruti'n" NM 4B Style.
Secret World HD	Clear "Secret World" NM 4B Style.
Shoreline RD	Play 1206 Songs.
Son Of Sun HD	Clear "Son Of Sun" NM 4B Style.
Stop HD	Clear "Stop" NM 4B Style.
Super Lovely MX	Play 618 Songs.