Where does "Tagoya" come from? At the start of the series (i think Episode 5 or 6), Sven teaches Eve to yell out "Tagoya" when she see's fireworks.


   later when Sven suggest to launch fireworks to lure Eden off-course, hearing the fireworks go off while within Eden Eve is yelling out "Tagoya" while on an elephant ignoring Adam


I am wondering, where does this thing about yelling "Tagoya" come from?
Are you sure you don't mean "Tama-ya!" rather than "Tagoya!"? It is very common for Japanese onlookers at a festival to loudly cry out "Tama-ya" and "Kagi-ya" when they see fireworks, instead of applause for the show. The words refer to two of the oldest, largest and most famous fireworks factories from the Meiji period (1868-1912).

I believe the plan is to so distract Eve with the fireworks and their surrounding customs that she'd be unaware of the changes being made behind her back.