Update time!
A new system has been implemented:

Inspired by Fire Emblem 4, I replaced affinity with "bloodline". (Blood for short, as shown on the stat screen.)
Along with new support bonuses for each bloodline, they also have their own skills. For instance:


The Kersey Bloodline (Adeline and Ann) boosts the character's strength cap by 2, as you can probably notice from the side by side comparison of Adeline and Milena's stat sheets.
Some of the skills affect stat caps and such, some are terrain based, and some are familiar skills, such as "Silencer".
Not every character has a notable bloodline, and those who don't have a notable bloodline have the following icon:

They still give support bonuses, however they don't have any special skills.
There are as of this post currently 14 bloodlines, double of the original total of affinities, and that doesn't count the "None" bloodline used for characters who don't have a notable bloodline. And likely there will be more added for some of the boss characters.