Yeah the menu issues are on my list of things to fix for the upcoming update. Appreciate the report though.
Undertale was definitely an influence for me but I wouldn't say that shows up in the battle system too much. You CAN interact with enemies but you'll be disappointed if you're expecting to be able to non violently end most encounters lol. That just isn't really a mechanic here.
Oneshot however I'm only really vaguely aware of so I can't say I really know much about it.