It is all explained there, i'll just fetch thaat part for you and send it below; helping exclusively one or the other doesn't preclude you from going for the neutral ending (as the first line implies).
"Neutral route/good ending: after the battle at the tavern, and seeing the chief (whoever invited you, based on who was less suspicious of you), go check on Thane at the tavern, if you invited him back at the end of part 3 of the war, or at the bull village if you didn’t; he’ll still be weak, but the important thing is receiving his bloody cloth from either Witer or a bull guard. Now you need to visit the painting in the bull temple, and this means you need to have the skull emblem (guaranteed after defeating the skull demon in “the first boss”) AND the soul emblem, which needs to be bought during the auction in “saving the master”, if you didn’t then... sorry, nothing you can do to find the truth now (note: if you don’t have the skull emblem instead, chances are you left it at the pawn shop in the demon city... hope you have enough bevocr to buy it back). If you do have both emblems, jump into the painting (if you haven’t been in there yet, jump in 3 times, so the event triggers), and don’t stop Thane the first time! You can stop him once he reaches the cave, but it is actually possible to click “let Thane go” 14 times to really let him go inside, just be careful, the options will invert to mess with you! This only changes the scene, the dialogue with the dragon a bit, and his painting of Thane won’t get ruined. Finally, go back and check the marked spot (“!”) on the map (...)"
There's even a small tab below that part that specifies what each choice does and the consequences of them, including which quests are altered later on (i tried to make it not too spoilery, still, all there, part 5 of the war, ask again if you need more details).