I was thinking to publish the prequel after the fourth or fifth volume of Pierro.
About the characters nationality all of them would be Japanese.
Ichika's name came unconsciously to me.
I thought I wanted to match the first letter of the couple's names
Some examples are
like Syaoran and Sakura from Cardcaptor Sakura of CLAMP
Sasuke and Sakura from Naruto of Masashi Kishimoto
About the names I was inspired by Naoki's name by the manga artist of Monster,Naoki Urasawa
Ichiru's name was inspired by Ichiru Kiryu,the twin young brother of Zero Kiryu from Vampire Knight of Hino Matsuri
In Vampire Knight Memories,the sequel Zero also mentions Ichiru.
Fate Zero anime were one of those factors who taught me to write a good prequel.