I am not saying Yoshi having fun other NPC's be impossible, but intent is more that it awakens during first sex (fullfillment of love) with person he is strongly attracted to. Anycase as Lust mentioned if your not interested to turn Shiori into serious love interest for Yoshi, Lust can probably create one from one his NPC's. Just thought to mention it so you can decide should you want take part in it or not.