Who is the Strongest Characters of Touhou? (in your opinion)

Celestial
Celestials (天人 tennin, literally "sky person", "heaven person" or "deva") are a higher class of hermits who reside in Heaven. An earthly hermit can become a celestial by further advancing their training, or a normal human can be transformed into a celestial directly.

Xian
Xian (仙, 仚 or 僊, Pinyin: Xian/Xiān/Xiān) is a Chinese word for an enlightened person, usually translated as "Taoist immortal". The Japanese word for hermits, sennin (仙人), is a borrowing of the less common term xianrén, which combines the characters for "xian" and "person". Xian develop roughly the same abilities as their Japanese counterparts, and are similarly long lived; they are described by Victor H. Mair as such:
They are immune to heat and cold, untouched by the elements, and can fly, mounting upward with a fluttering motion. They dwell apart from the chaotic world of man, subsist on air and dew, are not anxious like ordinary people, and have the smooth skin and innocent faces of children. The transcendents live an effortless existence that is best described as spontaneous. They recall the ancient Indian ascetics and holy men known as ṛṣi who possessed similar traits.

Shikaisen (Shijie xian)
Shikaisen (尸解仙, Pinyin: Shījiě xiān, Japanese: Shikaisen, lit. "Corpse Untie Xian") is a class of xian mentioned in Baopuzi. Considered the lowest level of immortality one can attain, it is required that a person "fake" their own death by substituting a bewitched object like a bamboo pole, sword, talisman or a shoe for their corpse or slipping a type of Death certificate into the coffin of a newly departed paternal grandfather, which deletes their name and allotted life span. Mortals who choose this route must cut off all ties with family and friends, move to a distant province, and enact the Ling bao tai xuan yin sheng zhi fu (靈寳太玄隂生之符 -- “Numinous Treasure Talisman of the Grand Mystery for Living in Hiding”) to protect themselves from heavenly retribution. So, the body is considered immortal, but immortality may only last as long as a sīmìng (司命) -- "Director of allotted life spans", lit. "Controller of Fate" allows, agents of death from the underworld can be fended off or life prolonging talismans found. Like hermits and celestials, it is not "true" immortality. Also like celestials, some shikaisen may also serve heaven.

Abilities: Resistance to Soul Manipulation and Non-Corporal (As her soul likely resides in some other object like most hermits), Memory Erasure/Existence Erasure (https://i.imgur.com/KvVeAYu.png), Soul, Mind, Emotion, Law and Physics Manipulation (All Youkai can control the world through physical and mental layers, the physical layer follows law of physics, the mental layer represents spiritual, emotion and mind), she is also a Oni so she her strength is very high

Memory/Existence Erasure, Resistance to Soul Manipulation, Feng Shui Manipulation,

Resistance to Soul Manipulation, Necromancy (Can control jiangshi), Portal Creation (Can pass through wall via opening a portal), Memory/Existence Erasure

Soul Absorption (The Sword of Hisou can absorb spirits and spiritual energy from its surroundings, converting them into energy), Energy and Chi Manipulation (Tenshi can release the energy absorbed by the Sword of Hisou in attacks and as beams of energy), Soul Manipulation and able to bypass intangibility (The Sword of Hisou reduces spirits it slashes into a scarlet mist that it can absorb, and it can completely destroy purely spiritual existences like phantoms), Resistance to Misfortune (Tenshi has so much fortune that it cannot be reduced, rendering her immune to Shion's attempts to bring misfortune for Tenshi), Mind Erasure, Earthquake

Mind Reading, Desire Empowerment, Divinity, Mind/Existence Erasure, Resistance to Soul Manipulation