Hardin fodder/robin build

I think Brazen Def/Res is a good option in itself, it gives a pretty good boost to your bulk, but imo Robin not only wants a defensive stat boost, but also an offensive one, if possible(not offensive as in “always go Fury”, but also skills like Steady/Warding Breath for the special cooldown reduction). That’s not to say it’s a very good option, though, so if you want to run it, go for it.

However, since I’m assuming you can only fodder one skill(because you don’t have more spare Hardins), Bold Fighter would probably be better for inheritance. It allows Robin to run a very powerful dual phase build, especially if you can give him a Breath skill and the Quick Riposte seal for maximum cooldown reduction shenanigans.

Bold Fighter is definitely better merited for Grobin. Pair that with Steady/Warding Breath (probably the latter since you have a Def boon), and he’ll be a fantastic tank who can double attack on his turn.