Brainstorming help: Why did my MC murder his grandfather?

A character of mine killed his mentor-- his grandfather, who was teaching him magic.

My original idea for this was: He caught his grandfather molesting his younger sister. He tried to report this to the authorities, who refused to do anything, because his grandfather was a very influential man. So he poisoned his grandfather instead.

I've decided this is a bit too dark and I'd prefer to leave sexual abuse out of my story.

So...

Why did my MC kill his grandfather?

Help me come up with some random, off-the-wall ideas. Or some serious ideas. At this point, I'm just throwing spaghetti at the wall to see what sticks.

 

This is a really difficult question because the options kinda depend on your protagonist‘s personality. Not every person is capable of every deed.

Here are some ideas that come to my mind:

• It was an accident. While practicing magic your MC couldn‘t control his powers and accidentally killed his mentor. When he realized he had actually killed him, he panicked and decided to hide body. (If you want others to consider him guilty, then either say that everyone thinks he did it because was the only one that close to his mentor even though they have no evidence or say that someone caught him burying the body.)
• He murdered for money. Because his grandfather is an influential person, he has gained quite a bit of money over the years. Your MC is an heir (grandson) and he wanted/needed the money, so he killed him and tried to frame one of his grandfather‘s business partners for it (successfully?).
• He is was forced to kill him. Either his grandfather was under a terrible spell or his own (as in the grandfather) spell tortured him so bad that the MC felt like he had to kill him to save him. Or maybe the MC was under a spell and used as a hitman of sorts. Maybe the MC was blackmailed. There are lots of options here.
• The grandfather wasn‘t a great man. His influence was gained through the exploitation of others. For example he could be involved in some sort of illegal trafficking, political schemes or just general criminal acts. Question is how does your character find out? Is he or someone close to him involved in this? Maybe his sister works for his granddad and pursues a "career" in crime which brings your MC over the edge.
• It was him or his granddad. His granddad attacked him first and he was just protecting himself. Here you would have to establish a motive for the grandfather.

This is all I can come up with on the spot. Hope it helps

 

The above list covers most scenarios, here is another.
The grandfather had disguised himself (here you'll need to come up with a reason why) and the grandson accidentally mistook him for someone else.

 

I'll expand on this one. His grandfather was trying to come up with a shapeshifting spell so he can disguise himself as an enemy of his family to discredit the enemy in front of his colleagues. The MC came in and then also being someone who hates and recognizes said enemy,wonders what the enemy was doing in his house and kills him.

 

As @Frieda said it's hard to really come up with reasons for murder without knowing the character.

But there is a line from a movie that I think could help the TC
"Well, possible motives for murder are profit, revenge, jealousy, to conceal a crime, to avoid humiliation & disgrace, or plain old homicidal mania. Right there in the manual."

Also just to be clear, Murder is different than accident, Murder is different than self-defense or defense of others.

There are a lot of reasons the protagonist might kill his grandfather but without knowing the protagonist their motives or their grandfather it's just random guesses... so I'll go with "Grandfather stole Protagonist girlfriend, protagonist cuts out grandfather's heart with a spoon." - you know the classic.

 

Wart Joram realised he was a character in a story, and if he learned magic he would never be able to enter the real world.
He wasn't expecting his grandfather to start teaching him Fire Shield in the process of over-toasting a waffle, and lashed out in haste to cut him off.
Without magic, how will he open the portal...

 

Of course, you could always have him commit suicide.


"I'm My Own Grandpa" by Dwight Latham and Moe Jaffe,


Now, many, many years ago
When I was twenty three
I was married to a widow
Who was pretty as could be
This widow had a grown-up daughter
Had hair of red
My father fell in love with her
And soon the two were wed
This made my dad my son-in-law
And changed my very life
My daughter was my mother
Because she was my father's wife
To complicate the matters
Even though it brought me joy
I soon became the father
Of a bouncing baby boy
My little baby then became
A brother-in-law to dad
And so became my uncle
Though it made me very sad
For if he was my uncle
That also made him the brother
Of the widow's grown-up daughter
Who, of course, was my stepmother

My father's wife then had a son
That kept them on the run
And he became my grandchild
For he was my daughter's son
My wife is now my mother's mother
And it makes me blue
Because, she is my wife
She's my grandmother too

Now, if my wife is my grandmother
Then, I am her grandchild
And every time I think of it
It nearly drives me wild
For now I have become
The strangest case you ever saw
As the husband of my grandmother
I am my own grandpa

 

Grandfather was replaced by a shapeshifter, and his real fate remains unknown.