If there is anything I hate about this game its the fact that you need to do things to be able to cast spell even though magic is your class. In dark souls games magic class wasn't bullshit like it is in this game, in dark souls you don't have to do "things" so you can cast a spell because your character starts with a basic spell or two. Thank you for the video its just that I hate this part of the game, thanks!
You can also get ninjutsu and onmyo magic points by finding ninja's locks and onmyo mage's lock from killing enemies. These items are purple rarity so they're pretty rare but they increase your skill points by 1.
Also when starting off it's better to invest your ninjutsu skill points in the bombs because they fill up your ninjutsu meter quicker than the shuriken.
Did you finish the mission & go back to this spot to farm? I got here & have just been farming amrita and proficiency points. Also Do I have to level up the omnyo to a certain point ?
I think I did completed the mission and went back to it. You can combine all your framing into one. Amrita, weapon proficiency points and along with Omnyo and Ninjutsu
Use fire, water or lightening amulets and those will give you the points to get the skills. You can find the amulets in the world or buy it from blacksmith
You can find water, fire or lightning amulets either during the mission or from blacksmith and keep using them and one you get a couple of points. Get any magic and use it to get more points