Now to Kenshin..He's a poor tortured soul gone tame in that cursed studentless dojo. We can just see the miserable life he leads...doing laundry, buying groceries, sweeping the wooden floors.. Let's get going before we go off topic any further...
Kenshin first started off as a very obedient student to Hiko Seijirou. He was learning the Hiten Mitsurugi Ryu techniques. Then one day, he started rebelling...well, not quite rebell, but he wouldn't continue learning because he claimed that there were many people outside suffering. Kenshin wanted to help them and left his kick ass master (^^;; Kenshin, what the HECK are you thinking??! BAKA DESHI!)
Afterwards, a man of the name, Katsura Kogoro recognizes Kenshin's talent in swordfighting and hires him to be one of his asassins. After several killings of government officials, Kenshin comes across Kyoto Soshida. Kyoto Soshida was Tomoe's fiance (yes, the same Tomoe that ends up with Kenshin later). Kyoto started protecting government officials because he wanted to prove his bravery to Tomoe. Anyhow, Kenshin kills Kyoto but since Kyoto had the will to live, he still managed to cut Kenshin across the left cheek...building the foundation of the cross scar.
Kenshin was shocked himself for receiving that slash but he gave little thought of it. However, there was a deeper meaning to the slash than he would have ever imagined. He learns this when he realizes how the slash would never heal, occasionally bleeding when he kills. He finally learns that the wound Kyoto gave him was out of hate because he knew that he would never see his fiance, Tomoe again. Kenshin was probably aware of this (does not know who Tomoe is yet), yet he killed Kyoto anyway.
After a while, Kenshin finally meets Tomoe. Tomoe was in a little bar drinking sake, trying to drain the grief from the death of her fiance. Afterwards, she leaves and comes across a short man who was fighting an opponent. Kenshin finally kills the opponent by slashing him straight down the middle of his body. The force from the strike left blood stains all over Tomoe. She says something about Kenshin being the cause of the bloody rain or something and she faints.