Random things that I'm including in my holy trifecta chuusigzai au
Dazai doesn't like wearing clothes and starts whining when Sigma forces an oversized t-shirt on him
(Chuuya also doesn't like Dazai wearing clothes)
Sigma has a spray bottle that he sprits at both Dazai and Chuuya when they 'misbehave'
Chuuya made a 'nest' in the cupola of the church
(Dazai has somehow dug a den under the confession booth)
Both Chuuya and Dazai can't be seen by anyone but Sigma (there are exceptions) in their 'base form'.
They can shape-shift though, and if their form is conceivable to the mortal mind and said mortal mind is given a convincing truth to believe they are then visible.
This leads Dazai to disguising himself as a nun on multiple occasions
They both have 'true forms', that are both terrifying and inconceivable
Sigma is armed to the teeth because there is still chance of people trying to rob the church since its a front for money laundering
Dazai is technically starving since he hasn't truly 'fed' in quite the while
There was a holy water incident that made Dazai disappear for a short period of time and not even Chuuya could find him
Sigma started buying regular wine out of his own pocket so that Chuuya and Dazai would stop drinking the communion wine
I will most likely add more...