Ok, so I won't go into to much detail in case my group sees this. But in the campaign that's happening there is about to be this big war. And my character has developed a bond with the party where he will sacrifice himself if it means they will live and win the war. I was thinking of homebrewing a spell he could use to essentially take out a decent amount of people, but at the cost of his life. But I wanted to know if there was something like that without homebrewing.

The wizard's School of Evocation Overchannel feature kind of does what you want.

Quote from Jesse_DND >>

The wizard's School of Evocation Overchannel feature kind of does what you want.

 Yeah, fireball centered on self. 

Ah um...ok, my character is a bard, college of Valor

Warding Bond buffs the defences of a party member and splits the damage between the 2 of you.

It's a Cleric spell so you'd have to get it with your magical secrets without any homebrewwing.

Maybe a make a higher version of that or say that for every 2 or 3 levels above 2nd you can target another creature. I'd also give it a bonus action to protect another ally on future rounds up to the restrictions in the homebrewwed rewrite.

Edited, Cheers Cybermind

Quote from Mikaos >>

Magical Secrets buffs the defences of a party member and splits the damage between the 2 of you.

It's a Cleric spell so you'd have to get it with your magical secrets without any homebrewwing.

Maybe a make a higher version of that or say that for every 2 or 3 levels above 2nd you can target another creature. I'd also give it a bonus action to protect another ally on future rounds up to the restrictions in the homebrewwed rewrite.

 
I think you mean Warding Bond?

Life transference and warding bond can fill the sacrifice self for others role. Wish can do anything if you are ready for backlash.

Short of those, you will have to ask DM and homebrew something.