Hyperion youkai needed
A youkai who represents the embodiment of authority, starts an incident intending to be the Gilgamesh of Touhou, wants to rule over every youkai ever existed and has remotely the strength to do so. However, it comes a time when even the Lord of Lords must bow to the shrinemaiden, but will this one bow? (Need genuine bad end)
Flasher youkai
better than SUPPA TENKO, a youkai that literally enjoys stripping. By that, she strips others as well as herself. Joke character.
Buddha Loli
Apprentice to Buddha, and likely as a name like Ananda or Subhuti, challenges Byakuren to a shrine building competition.
Titan
Ancient being larger than a mountain and was freed from holding the youkai mountain in place quite suddenly. The youkai mountain faces trouble unless the Titan returns to hold it in place again, or at least do something to support the youkai mountain from crumbling. Japanese lore has one called 'Da Tai Fa Shi' as in Lord Titan, a god known commonly to be recorded in Okinawan legend. Lord Titan is a mountain god much like the Titans were in Greek lore, and Lord Titan is responsible for 'Opening the skies and shaping the mountains while he pours the rivers into the seas' as was recorded in its legends.
A powerful youkai capable of moving mountains? and is a girl? awesome.
Samurai youkai
Not just your Youmu or Meira, these are dead spirits gathering to form a malicious being in the form of Samurais, dead ones. Long ago, it was believed that the Samurai warriors who died in battle especially during conquest missions and were not recovered and given proper rites would become these demonic beings.
Like the Lord of Sunken Spirits that inhabits the sea, whom has the power to kill anyone who dares look at its horrible rotten face, the Samurai legend would be the equal on ground. It is said these Samurai demonic bodies walk around battlefields looking for dead bodies to consume, and if anyone stupid enough to look it in the face, one would most certainly die from fright or a curse.
In legends, it was said only highest of priests with strictest of rituals may subdue it, and all this time the priests must never look it once, or they too will die. A great manner of disipline is needed for the Demon will likely do many things to force one to look at its horrible face in rebellion.
As a loli, I suppose this can be an extra boss, a boss that doesn't reveal its face until you defeat it.