I used to use PlainText long time ago. I just found out that they stop the support and somehow I couldn’t find it in the AppStore. I was looking for an alternative, and found this awesome site which lists all iOS Text Editors.
After trying several stuff, I found UpWord. It syncs to an Apps folder in Dropbox smoothly, including deleting files and adding files through and from other computer. It has this cool swipe gesture to change the format of a line. Awesome. It seems to have a reminder function as well, but being able to edit the text is enough for me.