suggestions to beat him in an easier way?

I hope this sticks somewhere near the top of this page.

The black rabite can realistically be beaten with any party, some just make it easier than others.

I'll try and hit all the abilities that really help and where you can find substitutes for them.

Heal light (Multitarget): Heal light is nice to have on the black rabite if only to give you two sources of healing and make you less item dependent. Multitarget heal light even more so. It's found on Light side Kevin and Duran as well as on Carlie no matter what.

A viable substitute for heal light are the healing items from the inns obviously and more importantly poto oils from the black market which give the person who uses them the ability to cast the item equivalent of multi-target heal light.

Saint sabre: This sabre allows you to hit harder on the black rabite and also counters the dark sabre the black rabite casts on you. It's found on Paladin Duran and on Light Light Carlie.

A viable substitute are papa poto's claws that can be found from killing papa potos and looting the chests they drop. They cast saint sabre on your party, if you do go in with these you will need at least 6 as the black rabite casts dark sabre on your party.

IMPORTANT: You must have some way to overwrite a sabre otherwise the black rabite will cast dark sabre on you and all your physical attacks will heal him. Saint sabre is one counter to this, a stardust herb is a second but dispels all other magical effects, the final counter is a specter's eye. This removes the dark status from the black rabite and means ANY elemental sabre can kill him, even dark.

Status up: Status up spells are great because they increase your damage on the black rabite and also up your defense against his completely rape attacks. The only character with stat up spells is Lise on her light side. Status up spells can be substituted with scales from the black market. 9 of each are usually a good idea since they don't cost very much to get.

Status Down: Status down spells are found on Dark Hawk, Lise and Carlie although only Carlie has 2 of the stat down spells as dark dark with demon breath. Status down spells can be substituted with Battum's Bee's Needlion's and Slime's eyes. These are very rare though so it's usually good to have a stat downer in your party

You will need one item:

The Chibbiko hammer: The Chibbiko hammer is the one item that will save you from the rabite. Status effects, like poison (Not stat downs or stat ups) don't stack. That means if you are poisioned, you can't also be asleep. The Chibbiko hammer casts the status Chibbiko on you, what's weird is that this status overwrites all others.

So if the black rabite puts a status effect on any party member, you can instantly remedy it by using the chibikko hammer on yourself, to turn yourself into a chibikko and them casting it again, to clear the chibikko effect. Keep it on you, the reason will become important in my guide. If you feel as if it's cheating then 9 piupiu grasses serve for a similar effect, although they are not multi target like the hammer.

Other stuff: Here are a few other things that will help you out.

Deadly weapon/Lunatic: Hawk as a nightblade or wanderer has these status down abilities. They reduce the maximum HP of a boss. This reduces the maximum HP of the black rabite as well and is WELL worth casting at the beginning of a fight. This effect can be substituted by a moon coin.

Counter magic: Hawk as a wanderer can learn counter magic. This spell is extremely useful in mitigating a lot of the black rabite's magical damage. It can be replicated using Pakkun Oils.

The fight: Most importantly, black rabite will counter ANY offensive spell on him. The type of counter is random, but often he will counter by summoning a level 99 Greater Demon. This is bad, very very bad. So set your allies to "Only cast level 1 techs" and make sure that you yourself also only use level 1 techs.

At the beginning of the fight, you want to immediately cast any status down spells on the black rabite. Why now? Well, if the black rabite counters with a level 99 greater demon then you can just walk out the room and reset the fight for minimal time loss. Remember, status down effects will stay with him for the ENTIRE fight so they're well worth getting in now. Once you've cast these, cast buff spells on yourself and set about beating the black rabite into a fine paste. Remember, don't cast spells on him or he WILL kill you.

Be sure to keep yourself healed, ensure that you use a healing item on any party member that goes below 200 hp or they are very likely to die.

The black rabite will start off slow, attacking you physically, maybe casting a few spells. It won't be that bad. Things really start to heat up when he casts a combination of evil gate and dark force on himself to heal. At this point he'll start casting anywhere from 2 to 4 spells in a row. If your party isn't at full HP for most of this he'll completely wipe the floor with you.

The big problems come when he either casts dark sabre on you, which you need to counter as mentioned earlier or he will turn all of your party into moogles. The way to counter the moogle spell is through use of the chibikko hammer to reverse the status effect.

This phase will continue on for a long while. I approximate until about 25% health.

At this point, the black rabite will cast ancient.

Ancient will hurt your party a lot. If you're not topped up it will screenwipe you. You need to keep your health in the 400s or so and you should be safe.

There's a theme here, it's called keep topped up. Don't worry too much though, you DON'T need heallight to do this, you can very easily maintain a decent amount of HP through good use of items.

After Ancient, the black rabite shouldn't be much of a threat. Keep going and you should be able to finish him off.

There have been stories of black rabite fights that have gone on for hours but I've never seen one last longer than about 10 minutes or so. So just keep at it and you should be able to take him down.