Some weirdo things...

[Krios]

Well iam new to onigiri so if you guys know something about those things post a reply

usami???(thats really her name!)
i was in a village the depressive one, and find her, i cant talk, see on minimap and my friend dont see her, she has a red and purple flower dress, bunny ears and earmuffs

drunken
i decided to see what happens when ´drunken´ and i had a surprise, my weapon dissapeared! i drinked 5 bootles

[Firon]

usami???(thats really her name!)
i was in a village the depressive one, and find her, i cant talk, see on minimap and my friend dont see her, she has a red and purple flower dress, bunny ears and earmuffs

If I had to guess, I'd say you've missed her quest from onigashima and your friend has done the quest so Usami??? has moved.

drunken
i decided to see what happens when ´drunken´ and i had a surprise, my weapon dissapeared! i drinked 5 bootles

0.0, that's.. never happened to me before.

[Chouhi Yokutoku]

clear Room of Rites, she will stand in the dungeon with a quest to finish the dungeon(any difficulty), afterwards you'll just talk to her in town and done.

the Onigashima Usami Mitsu npc has nothing to do with Yamataikoku "Usami ???"...
as far as i know, some of the quest(s) within Yamataikoku will trigger her appearance in Room of Rites first floor

regarding your friend not seeing her; its either he(she) already completed the quest with Usami ??? in Room of Rites or he(she) didn't progress through main quest far enough, so she didn't even appear in town.