1) defining mermaids

half fish
half human

2) luca (2021)

luca and alberto understand the struggles of choosing life between water and land
they are probably on the same family tree as mermaids

3) water activation

when luca touches water he turns back into a sea monster (mermaid)
this is just like the show h20: just add water,
which is about mermaids whose powers are activated by water

4) are sea monsters from luca mermaids?

yes its close enough
(source: me)

5) italy

luca takes place in italy, which is actually a real place in europe

6) luca likes pesto pasta

people who dont like pesto pasta aren't real to therefore luca is a real person.
by proving luca is a real person, we have also thus proven that mermaids are real
because we earlier proved that sea monsters are mermaids by the h20 theory