Those dark crimson tendrils were none other than the projection of the Abyssal Gaia. A small fraction of its power was seen when Havien was confronting Stella back on Earth, without really knowing what it really was.
But now, when faced with a similar situation, those memories he subconsciously tried to keep out of his mind, started bursting forth. Those memories filled him with disgust at the hypocrisy of these so-called 'good people' and truly angered him. This level of extreme rage, was in fact, the key to awakening this Gaia, but Havien being the cold-minded person he is, never truly raged at anything.
Back in the arena, While Havien was emitting the projection of his Gaia, Julius was getting deep chills and an extremely eerie feeling. He felt afraid of those tendrils, which looked truly ominous. But the biggest shock he got from this was the fact that those same tendrils were condensing onto his scythe
'He's condensing aura. But how?!'