Cure burning effect that character got in Suikoden II

I got a trouble with my character. In Suikoden II, whenever i attack random opponents, i always got the damage that my opponents got from my strike...

For example, i attack my opponent with 100 damage, with double strike, they got 200 damage, after i launch my attack to them, i got the effect of my attack with the same amount of damage as my opponents get. With the animation my character got burned. I don't know how to solved this. Did my character had an illness (poisoned, paralyzed ) ? Or that's just some weapons/armor effect ?

This is the scene when i got burned and got the damage that my opponent get from players attack ( in this picture, i got 43 damage, while my opponents got 86 damage ( double strike )

You have the fire lizard rune embedded in your weapon. It increases your damage by 1.5 times (modified by your fire affinity) but makes you take half of that damage on each normal attack.

To stop taking damage from regular attacks, either use a fire seal rune (first one is acquired in the highland camp that Jess sends you to prior to the fall of Muse) or remove the fire lizard from your weapon.

There is a Wiki page for all status effects from Suikoden 2.

It seems you are under the effects of "Boost", or there is an item that gives you Boost repeatedly.

Boost

Positive Status. 3 turns.

Attack strength doubles. Once Boost is finished, the user takes half the damage inflicted during Boost.

Your screenshot does not show what the character looks like normally. I'm also not familiar enough with the game to tell you what can be causing it.