diff --git a/keyserver/src/updaters/relationship-updaters.js b/keyserver/src/updaters/relationship-updaters.js
--- a/keyserver/src/updaters/relationship-updaters.js
+++ b/keyserver/src/updaters/relationship-updaters.js
@@ -198,6 +198,19 @@
         user1 = ${viewer.userID} AND user2 IN (${userIDs})
     `;
     await dbQuery(query);
+  } else if (action === relationshipActions.FARCASTER_MUTUAL) {
+    // We have to create personal threads before setting the relationship
+    // status. By doing that we make sure that failed thread creation is
+    // reported to the caller and can be repeated - there should be only
+    // one PERSONAL thread per a pair of users and we can safely call it
+    // repeatedly.
+    await createPersonalThreads(viewer, request);
+    const insertRows = request.userIDs.map(otherUserID => {
+      const [user1, user2] = sortUserIDs(viewer.userID, otherUserID);
+      return { user1, user2, status: undirectedStatus.KNOW_OF };
+    });
+    const updateDatas = await updateChangedUndirectedRelationships(insertRows);
+    await createUpdates(updateDatas);
   } else {
     invariant(false, `action ${action} is invalid or not supported currently`);
   }
@@ -313,9 +326,11 @@
   request: RelationshipRequest,
 ) {
   invariant(
-    request.action === relationshipActions.FRIEND,
-    'We should only create a PERSONAL threads when sending a FRIEND request, ' +
-      `but we tried to do that for ${request.action}`,
+    request.action === relationshipActions.FRIEND ||
+      request.action === relationshipActions.FARCASTER_MUTUAL,
+    'We should only create a PERSONAL threads when sending FRIEND or ' +
+      'FARCASTER_MUTUAL requests, but we tried to do that for ' +
+      request.action,
   );
 
   const threadIDPerUser: { [string]: string } = {};
diff --git a/lib/types/relationship-types.js b/lib/types/relationship-types.js
--- a/lib/types/relationship-types.js
+++ b/lib/types/relationship-types.js
@@ -36,6 +36,7 @@
   UNFRIEND: 'unfriend',
   BLOCK: 'block',
   UNBLOCK: 'unblock',
+  FARCASTER_MUTUAL: 'farcaster',
 });
 export type RelationshipAction = $Values<typeof relationshipActions>;
 export const relationshipActionsList: $ReadOnlyArray<RelationshipAction> =