ツチノコ探検隊 ～みゅうがいた夏～

"That summer, we met a miracle." When Sei, Tsumugi and Kaichi set out to find the "mythic snake" Sei already had a feeling that it was going to be a special summer. Out of nowhere they met the strange girl Myuu, an equally strange member of a secret society who went by "Sigma" and a robot-plushie Dantes, all part of a research team. Their curiosity piqued, Sei and friends chased the mystery, not knowing that by summer's end, their encounter would bring about an all-new capability for mankind...... Unknown beings. Aliens (?). A secret society-----The incredible self-discovery begins. [From DLsite English]