"Too Late To Regret"
Fire and Ice mana, which is always known for being parallel, totally opposite of each other's finally merged into one power.
The fire mana which was hidden inside of her past soul, as the past him continued to pass his mana into her dead to body to keep her warm returned to the current him.
Which contained the past memories.
The reason why he couldn't remember the past despite having the strongest powers was because he didn't had sufficient mana inside of him to remember the past or merge his past soul with the current body of his.
After turning back in time, both Jennifer and Alexander succeeded to control their younger self because of their strong powers and mentality.
But the past Cathain, who was weak in powers infront of his younger self couldn't do that.
His fading soul could only use his remaining powers to show some broken memories of their tragic ending to his younger self as visions, in this life to avoid the past ending.