You can only get S-Ranked Support with certain characters.
Romantic and Platonic S-Supports in FE: Engage (fully organized) : r/ fireemblem
Fire Emblem Engage Romance: The Ultimate Guide - Player Counter % %
Chapter 14: Showdown at Ailell Guide - Fire Emblem Warriors: Three Hopes - Neoseeker
Fire Emblem: Three Houses - How To Get 'S' Support
How to Earn Support Points and Increase Support Rank - Tips and Tricks - Gameplay, Fire Emblem Warriors: Three Hopes
Fire Emblem Engage - Tips And Tricks To Get You Started
How to get the Pact Ring & What S-Rank Support Does In-Game
Fire Emblem Engage Supports, including romance options and how to unlock Support conversations explained
FE3H, How to Raise Support Levels
Fire Emblem: Three Houses: How To Hack Same-Sex Marriages Into Your Game
How to Get S Rank in Every Mission in Fire Emblem Warriors Three Hopes
Fire Emblem Warriors: Three Hopes - Chapter 7: The Triumph of Valor Walkthrough - SAMURAI GAMERS
How To Get Support S-Rank In Fire Emblem Engage
Fire Emblem: Three Houses Authority Stat What is it, what does it do, how to increase? - GameRevolution