You would think it would not be that hard to buy a better lock or make a sign which warns people from the whole life sucking before it's too late and the packt is sealed. It also might lead to false expectations to write something like "sensual romance story" on the first page...
...I'm sure there are worse ways to go.
In fact, this is probably one of the best ways to leave the mortal plane.
That ending...Well, it's an endless cycle, but is that really a bad thing?
No it's not, just like Takahiro before him, Kiyoto eventually passed away from having his soul sucked out, and a new successor was chosen...most likely by Kiyoto.