From Omari's Sister:
"Pochama" is someone who likes soft and squishy things or someone who likes chubby people (A LOT). [...] In the story, the issue of being fat in high school is not dealt with in the expected fashion -- girl is EXTREMELY shy and cruelly bullied by skinny girls. This is about Tsugumi's and Tagami's progress as a couple.
All three chapters and the one-shot have been released in Japan.