Here is the full list of all 18 Sankaku Renai: Love Triangle Trouble achievements.
Cleared the common route.
Cleared the Shiina route.
Cleared the Nanaru route.
Cleared the Suzu route.
Cleared the Maho route.
Cleared the Cara route.
Cleared the Akane route.
Witness Maho comboing everyone else.
Discovered Nanaru's dirty secret.
Witnessed a tragic event.
Hit the mark.
Served some yakisoba.
Resisted the urges.
Got a glimpse into Akane's mind.
Confirmed Shiina's dedication.
Had some Ice Cream with Maho (and an extra).
Witness the Cook-off.
Lit up some fireworks with the gang.