Here is the full list of all 15 Summer Pockets achievements.
Use the Music Gallery
Use the CG Gallery
Complete Ao's scenario
Obtain the title, "Table Tennis God"
Participate in Islamon Battles
Complete the prologue
Play table tennis with Tenzen
Complete Shiroha's scenario
Complete Kamome's scenario
Complete Tsumugi's scenario
Complete the ALKA scenario
Complete all scenarios
Complete the Islamon Battles
Collect all four Celestial Beasts Islamon
Use the Character Gallery