I just (personally) think Maruki is an adult parallel to Joker.

Despite having minimal characterization, Joker innately helps people he meets, protects the weak (like the woman from his arrest), solves the problems of his confidants (most confidant links is you dealing with their problems, let's be real 😂), upholds justice, takes the fall for his whole team, doesn't share his burdens, etc.

Maruki is just an adult version of that, grown up and taken to the extreme. After everything he went through + positively reinforcing his 'savior' nature, the only difference is his methods and reach.

The savior complex / messiah complex is present in both of them in different degrees. It manifests differently within someone who is a teenager, vs. someone who is an adult with trauma (which, btw, Joker would realistically become, given enough time after p5r/p5s.)

I think that Maruki is someone Joker could have become if given enough time / conditioning.