Who do I invest in for normal blue missions? Koyuki or Wakamo?

I went from level 36 to 46 thanks to the double exp event

How much main story should I read in order to enjoy the event's story? It looks fun, I don't wanna skip

>>212076830
świnia to nie człowiek więc ciągne wajche

>>527295863
Koyuki
>gave you the worst voucher present
>have to heal her in challenge
>only good for her sex appeal and great choice in outfit
>actually not smart up in a club full of nerds