Kris isn't a mixture of frisk and chara however Kris, is the older chara. Now already your like "wait a damn minute that can't be" and to prove a point, let's go back to undertale genocide, and let's recall what happened to chara and Asriel.

Chara was the first human to fall into the underground, being adopted by the Dreemurr family, Chara wanted to get monsters out of the underground and killed themselves for Asriel to take their soul, only to be killed and Charas soul-shattering, effectively losing their determination.

In the genocide route, we the player take frisk on the adventure to slaughter all the monsters in the underground, we beat Asgore and kill Flowey to reach the absolute, the player has to choose to give up their soul. Now notice how I said the PLAYER and not frisk. At the absolute Chara states that she helped you finish the genocide route by giving you determination and a bit of extra power, however, due to the fact Chara's soul shattered they have no determination, so this leads me to my next point of interest.

Chara is leaching of frisks soul, Chara lost their determination after they died, so how does Chara suddenly just give frisk a bit of extra determination to finish the run, well simply put, they don't, Chara instead, feeds off the determination of frisk, now again, I say frisk, not the player, these are two separate entities. Chara drains some of the determination frisks gets when they level up or gain more LOVE.

Now we know that is not possible, or so we think, sans tells us that "LOVE to is an acronym, it stands for LEVEL OF VIOLENCE, it measures one's capacity to hurt." Though for frisk, it may be a different story, see when we kill every monster in an area, a save point says "DETERMINATION" and no not just because Chara is saying that you are determined, it's Chara telling you that you have gained more of said determination. This is how I think Love truly works. A soul, is a separate being from a vessel, although the vessel hosts the soul and does as the soul commands, the vessel has its own power separate to that of the soul. So when frisk gets a love, you dont get a love, frisk does, and with that extra determination frisk and not you is getting, chara can leach off it, eventually gaining the ability to manifest at the absolute. Now how does this tie back to deltarune? Well, lets go to the pacifist route, after we beat the genocide.

The pacifist route consists of you the player sparing all monsters in your way, and making friends, however if you decide to kill them all before this route, chara decides to take action in her own way. What this means is after the genocide, chara still has your soul, the PLAYERS soul, however, this is where it gets complicated. Frisk now has a soul, and even though we can choose what frisk still does, we are now not the player, but we are frisk now. Frisk is under influence of chara still, that's why at the end of pacifist run at a post-genocide run, we see chara, looking up at the screen and laughing. AND THIS is where deltarune comes into play

Deltarune: deltarune is about a kid named Kris, and their imaginative adventure to the darkner world with Susie and Ralsie, the three travel through the darkner world to restore light to the well. And through the game, us the player has no choice in this game, no matter what we do, it makes no difference to the story or ending, and the ending always ends with Kris, throwing you, the player into a cage, and glaring at the screen with a knife.

Now to make a bit of sense before I go to why Kris is older Chara. When playing Deltarune, at the character customization screen, we can't choose what Kris looks like, being told we have no choice, now most people would assume that it is gaster telling us that, but I believe it is actually Kris/Chara telling us that. Here is more detail. Early in the game Susie asks us if we want to do the project or if you both want to do it, when you choose your option it would seem like Susie cuts you off, what I think happens is that Kris is purposely trying not to say what you want them to say. That is why Susie seems to cut us off. Later in the game when Kris takes his soul out, we see that we can still move the soul, but we can't seemingly control Kris. And the reason is a bit sadder than you think. Kris is resisting YOU.

Now on game theory, Austin states that Kris has PTSD on some kind of level, however, I did not think it was in the way that they thought it was. We have a lot of info about how Kris has PTSD you should watch game theory about that, its really interesting. However I think it could go into a bit more detail. Now this is another big throw, but when Chara in undertale dies, they not only killed themselves, but they also watched as their adoptive brother dies too. That would also be enough to give somebody PTSD, and now this is where I link the two stories together.

At the end of the pacifist route after a genocide route, we see chara stare at the screen and laugh, and if you think this is so they can kill everybody your damn right, they need more determination, and here is why. Its because they are trying, to build something. A world. And that world is deltarune. Just think about the similarities between kris and chara. Kris is the only human in their town, chara is the only human in the underground, kris and cahra were adopted by the dreemurrs (most likely so toby fox did not have to make a totally different family) and they both have some kind of power to override the power a player has. Chara created deltarune for them to be able to live the perfect life they wanted. Though, it seems to not end out as planned as asriel still leaves Kris, and toriel and asgore still get divorced. And the fact that Kris was originally quiet anyways is that they most likely had trauma to the fact that they lost everything they loved in the other world, and they are afraid of losing it again.

Long story short, Chara takes the players soul in hopes of gaining the powers of the player, they do for a while, creating their own world and changing the vessel of frisk to make it look more like chara. Chara creates the world and is still distraught by the things that happened in their past life. Toriel and asgore get divorced and Asriel leaves. Leaving Kris to feel alone. That is when Deltarune starts. The player has re-awakened and is trying to again, mess with Chara/Kris's life. However, Kris with the power they have tries their hardest to resist the player, however, still needs them to do dodging. And Kris at the end of the game takes out YOU the player from their body and is slowly gaining their own determination. And that is why they are able to still manifest. I do not think Kris held out his knife at the end because he was indicating he was gonna kill everybody. I think it was a warning to the player. Because in the most recent teasers for chapter 2, we really dont see any way that kris is gonna try and kill susie and ralsie in the future.

So I think, that the story of deltarune and the story of undertale/deltarune isn't about you. Its about chara and kris and their attempts to stop the player. And another reference to what Austin said in game theory he says that the hero is not technically the main character. in undertale that is true, the hero is not the main character. And in deltarune it is the same, kris is not the protagonist that we play as, the soul is the protagonist, and we. . . are not really the best protagonist then.

Tell me what you think of this theory and sorry for it being so long.