In front of Solar, theres a sign that says theres certian tricks to weaken her. What are they? (Also how do you unlock the NSFW scene with her?)

For the first question, there's an area where you could pour something to ruins the ecosystem(it's hidden though but there's some area that the tree is not really there.

For the second question, you need to have a balls, for some reasons your balls got destroyed if you die, so you need to attach new one on the bonfire.