[@Thayr]

I'm not sold on the Cornucopiad as the Chapter name and will switch to using it as a reference to the command staff. As for the speciality I wasn't exactly sure how to word it so I'll spill it here and see what I can do with it.

If they had a true Specialty it would be mortal morale enhancement, the Sons of the Harvest have an incredibly tight bond with the mortals of their Homeworld and the citizens of the imperium as a whole, seeing themselves as shephards and humanity as their flock or the bees to their keepers. So when a company goes to war its to either protect population centers from encroaching hordes, facilitate the evacuation of civilians if the planet should fall, or avenge them should they find nothing left to protect.

On the flipped side of the coin, the Sons of the Harvest inspire the flock so much that once mewling mobs get whipped into mobs of wild zealotry in the the defense of their homes.

I guess on an individual level the Adtartes of the Sons of the Harvest are great duelists, accurate shots even by astartes standards, and patient/stubborn to dig in on the defense, but as a Chapter they don't really shine in the eyes of the Highlords of Terra or their Astartes peers in ways that they would value.

As for The Coming Rain my idea for it has always been that it's oversized and undergunned, in terms of ship to ship combat at least. It's Strength comes from the fact that it holds so much supplies in reserve with an ability to craft arms and armor, grow food and medicines through sophisticated hydroponic systems, and support a staff of Chapter Serfs who are willing to jump into the fires of war as eagerly as their lords and masters. On paper the Mechanicum are... fine, with The Coming Rain since, officially, it was an Explorator fleet Archmagos that created the thing, but the fleet was lost and the Techpriests who inhabit it now have been fully naturized after 2,000 years of service. Off the books they'd really like to peel it apart because the launch bays and drop pod launchers are more advanced than their counterparts.