Clorinde's Demo has broken a year-long streak
Clorinde is the first character in over a year with no cameos of another playable character in their demo. I'll list them in reverse-chronological order for reference (with notes on updated ones at the bottom of the list).
- Sethos: Tighnari (voice), Wanderer (voice), Faruzan, and Cyno
(voice)(see update) - Arlecchino: Lyney, Lynette, and Freminet
- Chiori: Lyney, Lynette, Navia, and Kirara
- Xianyun: Ganyu and Shenhe
- Gaming: Traveller (Aether)
- Chevreuse: Charlotte
- Navia: Charlotte and Lynette
- Furina: Charlotte, Tartaglia, Navia, Neuvillette, Lyney, Lynette, Freminet, Clorinde, and Wriothesley
- Charlotte: Traveller (Aether), Klee, Cyno, Tighnari, and Collei
- Wriothesley: Sigewinne
- Neuvillette: Furina
- Freminet: Lyney and Lynette
- Lynette: Lyney, Charlotte, and Freminet
- Lyney: Lynette and Freminet
- Kirara: Amber, Qiqi, Kuki Shinobu, Arataki Itto, Kaveh, and Yae Miko
- Baizhu: Qiqi
- Kaveh: Cyno, Nilou, Dehya, Candace, Wanderer, Alhaitham, Layla, Faruzan, Dori, Tighnari, and Collei
- Mika: Jean and Klee
- Dehya: Candace
- Alhaitham: Kaveh, Tighnari, and Cyno
- Yaoyao: Cloud Retainer (illuminated beast form) and Qiqi (see update)
- Faruzan: Traveller (Aether)
The one previous to Alhaitham's was Yaoyao's, which did have Cloud Retainer in her illuminated beast form (and not as Xianyun). If you wish to count this, then the list only also includes Faruzan's which had Traveller (Aether) as Wanderer's had no cameos.
Update: u/MSDTenshi pointed out in their comment that Qiqi appears in Yaoyao's demo. I've added Yaoyao's and Faruzan's to the list above. Wanderer's had no cameos.
Update: u/decemberiris pointed out in their comment that Cyno can be seen seated with his back to the camera during his line in Sethos' demo. I've updated the list accordingly.