Hm...
The Hortons (and Valkyrie as well as her husband Evan O'Neill - which sounds more badass than Evan Horton) could be secret characters?
LS ZER0 has no true final boss (Evan dies fighting Aidan Flamberge), though LS has Invidia and Nemesis, who revive Valkyrie when defeated (Evan and his twin Areva get revived later in 2015).
And apparently Valkyrie has twins born in 2019 as well.