Harry Potter and Code Lyoko.
In his first year, Sirius comes across a secret passage way and finds a powerful magical object that is the magical version of the super computer, he activates it. When he next visits there Lilly and Severus follow him and together they work out what it is, they vow to keep it a secret until they find out what it is. The evil entity that comes from the object soon starts to cause havoc and so the three find they have to go into the world created by the object to defeat the entity, Lilly is a descendent of the creators of the object so she deactivates what the entity is using for its attack. The three pretend not to like each other in the presence of others to keep suspicion off of them.
The world is called Mayoko and is similar to Lyoko but more magic based, the evil entity is called Z.A.N.A . Z.A.N.A possesses things in the real world by accessing giant stones covered with runes. Mayoko is accessed through scanners that use magic and the magical object emits a holographic interface to use it.
Sirius' weapons are two guns with 20 shots each and gauntlets that create claw of energy to slice at his opponents, he is faster and more agile.. He has black dog ears and a tail, he wars a black leather jacket, blue jeans that are ripped, mountain boots and a dog collar around his neck.
Severus' powers are similar to the green lanterns but more limited and less powerful, he can fly and create and weapon he wants out of energy but if he or his creations take enough hits his powers short circuit and stop working for a while. He wears a black trench coat, gray shirt, black trousers, red and gray trainers and metal wrist guards.
Lilly's weapons are two double headed axes and an endless amount of wire that comes from a small pocket on her belt, she can also teleport ten times on every visit to Mayoko. She wears a blue t-shirt, a red vest, black leggings, metal shin guards, rollerblades, a green scarf, bandages for armbands, a green helmet and black aviator goggles.