Highlighted weapons are free options.
Gorou is a Support character that can give increasing buffs to your party members from his Skill and Burst based on the number of Geo characters in your team (capped at 3). Casting his Skill sets up a banner which gives Flat DEF (1 Geo), Interruption Resistance (2 Geo) and Geo DMG Bonus (3 Geo) for your active character standing inside the banner radius.
Casting his Burst creates a field following the active character which deals periodic damage and offers the same bonuses given by the [[ability:skill, destroying any placed banners in the process, it also pulls in nearby Elemental Shards created by Crystallize reactions.
Due to his kit focusing on buffing DEF% and Geo DMG, he's a specialised support geared towards Geo DPS that scales with DEF, such as Noelle or Arataki Itto. He can see niche use at [C6] with other Geo characters as well.
[C2] extends the duration of Gorou's Burst from 9 seconds to 12 seconds if you can obtain the required Crystallize shields. This allows his teammates to gain the 3 Geo 15% Geo DMG bonus for a longer duration, so it's preferable to use Burst as your last ability before swapping into your DPS.
DEF% Main stats and substats (and potentially a Healing Bonus Main Stat on Circlet) can be considered at [C4] due to being able to heal the active character based on his DEF during Burst. This is useful if you plan to use him as a solo healer.
CRIT Rate circlet and substats can be considered when Gorou is using to trigger the passive comfortably.
Energy Recharge substats can usually be more important than getting the right Main Stat, as Gorou's damage contribution to a team is negligible, while being able to get Energy for his Burst is a lot more important.