The arrow coming at Hildegunde would still be a regular arrow, but abnormally faster than the prior one loosed. Apart from that, it appears to be a regular arrow.
As for Kiimos Trelle, it would be known to those who keep up with either matters of mercenary guilds or modern day Umbralist politics as a silver rank mercenary company primarily keeping to the Northern Neutral Territories. To any who know of them, they’d be known primarily for originally being refugees that fled Western Loustrain - a country on the western continent of Ventric - during the Five Year Apocalypse. After surviving, they’ve since dedicated themselves to cleaning up Umbralist remnants or making them convert through force to the ways of Astra. If someone knew Loustrainian or otherwise heard it as a fun fact, they would additionally know that Kiimos Trelle means “Most Spiritual of the Trinity Trail” in Loustrainian.
As for what mercenary ranks mean, I won’t type up a big thing about that right now, but mercenary companies are divided and ranked in the conventional currency: copper, silver, gold and platinum. Companies and individual mercenaries are ranked separately by these, and a company’s rank is determined on a combination of their deeds and the amount of members of a specific rank they hold. It’s also held as tradition that when a mercenary dies, they’re buried with a pouch of their rank’s coin on their chest.