Jack is a kitten and is going to hog play time. You have to get them to associate each other with good things. Rub Jack all over with a clean cloth, and rub Asher all over with a clean cloth, then put down treats on the cloths - put the "Jack" smell cloth down for Asher, and put the "Asher" smell cloth down for Jack. Do this at the same time every day.
The best way to introduce is to keep them separate initially and let them meet gradually, but it's a little late for that.
For now, I'd play with them separately, and I'd give Asher loads of extra attention. Any time Jack comes in the room, give Asher a treat, or get out new toys and toss one to each of them. Asher needs to learn to associate Jack with good things, and this will help - it's a party every time Jack shows up! If Asher loves being petted or being brushed, you can do this too.
Since Asher is the one that needs to make the most adjustment, if you free feed, I'd put a cloth with Jack's smell on it under the food dish. If you feed them wet food, I'd do the same cloth trick for each. Put Asher's smell under Jack's food, and put Jack's smell under Asher's food.
There's going to be hissing, growling and fighting. This is normal. Let them work it out. If ears are back, tails are agitated - then maybe give a loud clap (or shake coins in a can) to break it up. But one of them is going to have to establish dominance, and that'll take some time.