We nerf all champions, except Riven and Vayne. - Rito balance team
Riven over 50% winrate for 8 years straight. The champion with the most OTPs in Master+. The champion that dominates lane from level 1 and builds one item and becomes a super tank becoming unkillable. The champion that has 4 dashes with a stun with a spammable shield. The champion that has execute damage in an AOE.
Vayne over 50% winrate for god knows how long but now over 53% win rate with a 24% play rate for over 3 months. Starts scaling from level 6 onwards with the Q refund bullshit. Permanent stealth with her ultimate with mobility, good luck trying to right click her. Gets extended ultimate duration just for damaging champions not for killing them. Destroys squishies in 2 hits and destroys tanks because 14% maximum health true damage every 2 attacks is balanced in Rito's eyes. Self peel with a knockback and stun.
buffs reeeeeEEEEEEEEEEEEEEEEEEEEEEEEE

and consistently wins with him, he'll probably be gutted before LCS is even over.
on your team since they PHYSICALLY couldnt kill him.
Nerfing is also buffing the counter to something to a certain extent. If you nerfed health, then you buffed damage, if you nerf everything then everything is equal. If you nerf ONLY damage, then healing becomes broken and so on.