Beat the guy legit!
You only need the 4D sword.
1st phase. The boss always starts with a basic attack salvo. Do a dodge past him real quick and you should be able to avoid the rest of the strikes by walking. In this stage it's 4 swings. When he's finished, land a full combo yourself onto him, then dash into another combo. The boss won't accept more than 12 hits in one go though so 3 full combos is your limit before he counters. Once you finish your combos immediately dash away and get some good distance. This will help you react to what he does next. If it's lightning, then just dash away from him and stay out of the yellow field. If it's fire or ice, which you'll learn to tell coming by his actions or sound prompts eventually, just dodge to the side and make sure to keep your space. When he starts running at you, then he's trying to launch his melee combo. Just dodge and then strike. Somewhere between 6-9 full combos on him will be enough to end a phase.
2nd phase. The boss will also start with an attack salvo just as before, but I wanna say this salvo has 5 swings to it now and watch out because the basic melee combo always starts with him warping next to you first. The second move will always be him rushing to the middle and making a ton of fireballs and then 6 beams of light that fire straight out. Just go to the edge of the arena and you should be fine. Be prepared for him to teleport to you to begin striking again though. The other attack this form has is when he creates a series of light beams then fires them at you. Just pick a direction and keep holding dash that way until the attack ends and you should be fine.
3rd phase. The boss doesn't move around so much here. If the boss raises his sword and slams it into the ground, then it's a large area spinning laser attack. Do your best to turn into a 4d cloud and then get as much air as you can. I never got this off without a hitch and I think the attack can be dodged by timed jumps too but I can't say. Also, don't float directly above the barrier covering the boss as all the space above him is a hit area too. Pray you don't have the boss use this attack too often. Another attack is some white sketch-like version of the boss will appear and then fade away. Just start dodging. These copies will come out of nowhere to strike at you. They don't hurt too bad though thankfully, but there are a lot of strikes to dodge. The worst part is that the boss will prep their next attack before these have stopped attacking you so be ready. The third attack this boss can use is when he raises his sword high into the air and particles charge up around it. When he's done he'll swing it down and a GIANT burst of energy will move forward. If it connects, it's all your HP unless you have a second chance. Dodge this by keeping some distance. The swing will track you during the charging, but right before the strike you can dodge diagonally toward him. If the angle's right, the beam will miss you. Then just dash again back towards him. The stunt should make a > shape. At this point the boss can be hit by your combos. Have at it.
4th phase. The boss gains an invulnerability shield. 3 crystals will spawn and when they break the shield will drop for a set time. The boss has no new attacks, but has access to every single attack prior to this form. Break the 3 crystals while keeping your defensive game up then wait for the same vulnerable moments in the previous forms to get that damage in. The shield restores on a timer by the way so you can't be certain you'll get your full 3 combos in like before. Shave him down to nothing and experience the ending. Funny things happen. It's a gas.