You can only get S-Ranked Support with certain characters.
Fire Emblem Warriors: Three Hopes - 6 Tips for Getting S Rank
Fire Emblem Engage romance guide: how to romance and character list
Fire Emblem: Three Houses Review. Buy the game here…, by George Dutton, Finite Guild
How To Get Support S-Rank In Fire Emblem Engage
How to Increase Fire Emblem Engage Characters' Supports Rank Guide
New Supports in 'Fire Emblem Warriors: Three Hopes
Fire Emblem Engage Romance: The Ultimate Guide - Player Counter % %
Fire Emblem: Three Houses Authority Stat What is it, what does it do, how to increase? - GameRevolution
How to gain support ranks quickly in Fire Emblem Engage
Fire Emblem: Three Houses S-class romance support guide - Every potential relationship listed
Fire Emblem Warriors: Three Hopes - Chapter 7: The Triumph of Valor Walkthrough - SAMURAI GAMERS
How to get the Pact Ring & What S-Rank Support Does In-Game
Progression of the Support Ranks - Fire Emblem: Romance guide, conversations and raise support level - Millenium
Fire Emblem: Three Houses' is a slice of epic life
Fire Emblem Engage: How to Reach Support Rank S