In the demo version, Ichirin refers to someone (Byakuren?) as 姐御 (anego) and 姐さん (ane-san or nee-san). Both terms are variants on "elder sister", but these versions usually mean a female superior who is not one's real sister, such as a female gang boss.
Ichirin's outfit closely resembles that of a Buddhist nun's, which is appropriate, considering her ability.
Ichirin's inspiration may come from the second volume of Shigi san Engi. In the story, Daigo Tennou becomes dangerously ill one day, so his subjects visited Myouren to beg him to come and pray for the emperor. Myouren rejected their request for some reason but proposed that he would do it at his temple and he would inform them when he finished. After approximately three days passed, a flying stranger, Ken no Gohou (剣の御法) appeared near the court, who implied the end of Myouren's praying. After that, the emperor recovered very soon. His outfit is; a sword in one hand, numerous blades around his neck, and he flew on the wheel very similar to a dharmacakra, followed by wind or clouds. We could say that Ichirin is most derived from the dharmacakra called "hourin" (宝輪) in Japanese, which has one of the same kanji in Ichirin's name (一輪). Also, Myouren's sister, Byakuren's inspiration, gave him a cloth to wear as a gift and the cloth was stored in the Soaring Vault (Tobikura, 飛倉), the inspiration for the Palanquin Ship. These correspond to the points that Ichirin's wearing a hood and is the guardian of Palanquin Ship. Also look at these pictures.
The characters for Unzan's name mean "Clouded Mountain" or "Mountain of Clouds".
Unzan being purple is a reference to the purple cloud leading to where Myouren was.
There is an old Japanese tale about a tsukumogami (a youkai born from an old object attaining a spirit of its own after being around for 100 years) named Ichiren Nyuudou, which was a tsukumogami born from a Buddhist rosary. ZUN may have based this character off of the tale.
In an interview with ZUN, he states that Ichirin isn't the only one that can hear Unzan. Rather, he's just shy and tends to whisper, so Ichirin repeats what he said to others "Like a spokesperson".