This doujin is about Kamina being another virtual lifeform created by Antispiral to monitor on the Spiral races. When he died, he got summoned back to the Antispiral mother planet, and told Nia would take his place, being made of the same material and all. Then, to escape destruction at Antispiral's hands, he made his existence uncertain, keeping him effectively in limbo until Simon would think strongly enough of him to make his existence certain. Then at the end, he gives to Nia his remaining Antispiral power so that she would hold out three more days. This is why Nia calls Kamina "Oniisama" and why Kamina kisses her.